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                        Exit Status
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                        Interactive vs Non-Interactive Shell
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                        Login vs Non-Login Shell
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                        etc
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                            <b>3.</b>
                        
                        Test
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                            <b>3.1.</b>
                        
                        Operators
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                            <b>4.</b>
                        
                        Subshells
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                        Process Creation
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                            <b>5.</b>
                        
                        Commands
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                            <b>5.1.</b>
                        
                        Builtin Commands
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                            <b>5.1.1.</b>
                        
                        read
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                            <b>5.1.2.</b>
                        
                        printf
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                            <b>5.1.3.</b>
                        
                        eval
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                            <b>5.1.4.</b>
                        
                        getopts
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                        Keyword Commands
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                        Compound Commands
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                        Special Commands
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                            <b>5.4.</b>
                        
                        expr
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                        grep
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                            <b>5.6.</b>
                        
                        find
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                            <b>5.7.</b>
                        
                        xargs
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                            <b>6.</b>
                        
                        Arrays
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                            <b>7.</b>
                        
                        Shell Metacharacters
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                            <b>7.1.</b>
                        
                        Precedence
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                            <b>8.</b>
                        
                        Expansions and Substitutions
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                            <b>8.1.</b>
                        
                        Brace Expansion
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                            <b>8.2.</b>
                        
                        Tilde Expansion
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                            <b>8.3.</b>
                        
                        Parameter Expansion
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                            <b>8.4.</b>
                        
                        Arithmetic Expansion
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                            <b>8.5.</b>
                        
                        Command Substitution
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                            <b>8.6.</b>
                        
                        Process Substitution
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                            <b>8.7.</b>
                        
                        Word Splitting
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                            <b>8.8.</b>
                        
                        Filename Expansion
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                            <b>9.</b>
                        
                        Job Control
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                            <b>9.1.</b>
                        
                        Session and Process Group
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                            <b>9.2.</b>
                        
                        Process State Codes
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                            <b>9.3.</b>
                        
                        TTY
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                            <b>9.4.</b>
                        
                        Mutual Exclusion
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                            <b>10.</b>
                        
                        Redirections
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                            <b>10.1.</b>
                        
                        File Descriptors
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                            <b>10.2.</b>
                        
                        &lt;&lt; , &lt;&lt;&lt;
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                            <b>10.3.</b>
                        
                        Pipe
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                            <b>10.4.</b>
                        
                        Named Pipe
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                            <b>10.5.</b>
                        
                        Buffering
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                            <b>11.</b>
                        
                        Signals and Traps
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                            <b>11.1.</b>
                        
                        kill
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                            <b>11.2.</b>
                        
                        trap
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                            <b>11.3.</b>
                        
                        Signals Table
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                            <b>12.</b>
                        
                        Command Aliases
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                            <b>13.</b>
                        
                        Command History
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                            <b>14.</b>
                        
                        Command Completion
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                            <b>15.</b>
                        
                        Readline
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                            <b>16.</b>
                        
                        Colors and Prompt
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        <li class="chapter " data-level="17" data-path="shell_variables.html">
            
                
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                            <b>17.</b>
                        
                        Shell Variables
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                            <b>17.1.</b>
                        
                        Positional Parameters
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                            <b>17.2.</b>
                        
                        Special Parameters
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        <li class="chapter " data-level="18" data-path="shell_options.html">
            
                
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                            <b>18.</b>
                        
                        Shell Options
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                            <b>18.1.</b>
                        
                        Command-line options
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                            <b>19.</b>
                        
                        Debugging
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                            <b>20.</b>
                        
                        Locale
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                            <b>21.</b>
                        
                        sh
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                        <h1 id="eval">eval</h1>
<blockquote>
<p>eval [ arg . . . ]</p>
</blockquote>
<p><a href="exp_and_sub/command_substitution.html">&#xBA85;&#xB839;&#xCE58;&#xD658;</a> &#xACB0;&#xACFC;&#xB85C; shell &#xC5D0;&#xC11C; &#xC2E4;&#xD589; &#xAC00;&#xB2A5;&#xD55C; &#xBA85;&#xB839;&#xBB38;&#xC774; &#xB098;&#xC628;&#xB2E4;&#xBA74; &#xADF8; &#xBA85;&#xB839;&#xC740; &#xAE30;&#xBCF8;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xC774; &#xAC00;&#xB2A5;&#xD569;&#xB2C8;&#xB2E4;.
&#xD558;&#xC9C0;&#xB9CC; &#xBA85;&#xB839;&#xBB38;&#xC774; &#xC870;&#xAE08; &#xBCF5;&#xC7A1;&#xD574;&#xC838;&#xC11C; &#xD30C;&#xC774;&#xD504;&#xB098; redirections, quotes &#xB4F1;&#xC774; &#xC0AC;&#xC6A9;&#xB41C;&#xB2E4;&#xBA74;
&#xC774;&#xC81C;&#xB294; &#xADF8; &#xBA85;&#xB839;&#xBB38;&#xC740; &#xC2E4;&#xD589;&#xD560; &#xC218; &#xC5C6;&#xAC8C; &#xB429;&#xB2C8;&#xB2E4;.
&#xC65C;&#xB0D0;&#xD558;&#xBA74; &#xBA85;&#xB839;&#xBB38;&#xC5D0;&#xC11C; &#xC0AC;&#xC6A9;&#xB418;&#xB294; shell &#xD0A4;&#xC6CC;&#xB4DC;, &#xBA54;&#xD0C0;&#xBB38;&#xC790;&#xB4E4;, quotes &#xB4F1;&#xC740;
<a href="expansions_and_substitutions.html">&#xD655;&#xC7A5;&#xACFC; &#xCE58;&#xD658;</a> &#xC774;&#xC804;&#xC5D0; &#xD574;&#xC11D;&#xC774; &#xC644;&#xB8CC;&#xB418;&#xAE30; &#xB54C;&#xBB38;&#xC785;&#xB2C8;&#xB2E4;.
&#xB530;&#xB77C;&#xC11C; &#xC774;&#xC640; &#xAC19;&#xC740; &#xACBD;&#xC6B0;&#xC5D0;&#xB3C4; &#xC2E4;&#xD589;&#xC774; &#xAC00;&#xB2A5;&#xD558;&#xAC8C; &#xD574;&#xC8FC;&#xB294; &#xBA85;&#xB839;&#xC774; eval &#xBA85;&#xB839;&#xC785;&#xB2C8;&#xB2E4;.
eval &#xC740; &#xC778;&#xC218;&#xB85C; &#xC8FC;&#xC5B4;&#xC9C0;&#xB294; &#xC2A4;&#xD2B8;&#xB9C1;&#xC744; &#xD55C;&#xBC88; evaluation &#xD55C; &#xD6C4;&#xC5D0; &#xACB0;&#xACFC;&#xB97C; &#xB2E4;&#xC2DC; &#xBA85;&#xB839;&#xBB38;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xD569;&#xB2C8;&#xB2E4;.  </p>
<pre><code class="lang-bash"><span class="hljs-comment"># &#xBA85;&#xB839;&#xCE58;&#xD658; &#xACB0;&#xACFC;&#xB85C; ls -l &#xC2A4;&#xD2B8;&#xB9C1;&#xC774; &#xCD9C;&#xB825;&#xB418;&#xBBC0;&#xB85C; &#xC815;&#xC0C1;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xB41C;&#xB2E4;.</span>
$ $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;ls -l&apos;</span> )  
total <span class="hljs-number">4168</span>
drwxr-xr-x  <span class="hljs-number">2</span> mug896 mug896    <span class="hljs-number">4096</span> May  <span class="hljs-number">3</span> <span class="hljs-number">16</span>:<span class="hljs-number">53</span> Desktop
drwxr-xr-x <span class="hljs-number">45</span> mug896 mug896    <span class="hljs-number">4096</span> Apr <span class="hljs-number">26</span> <span class="hljs-number">20</span>:<span class="hljs-number">59</span> Documents
. . .

<span class="hljs-comment"># &#xBA85;&#xB839;&#xBB38;&#xC5D0; &#xD30C;&#xC774;&#xD504; &#xBA54;&#xD0C0;&#xBB38;&#xC790;&#xAC00; &#xC0AC;&#xC6A9;&#xB418;&#xC5B4; &#xC815;&#xC0C1;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xB418;&#xC9C0; &#xC54A;&#xB294;&#xB2E4;.</span>
$ $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;ls -l | wc -l&apos;</span> )
ls: cannot access <span class="hljs-string">&apos;|&apos;</span>: No such file or directory
ls: cannot access <span class="hljs-string">&apos;wc&apos;</span>: No such file or directory

<span class="hljs-comment"># &#xC774;&#xB54C; eval &#xB97C; &#xC0AC;&#xC6A9;&#xD558;&#xBA74; &#xC815;&#xC0C1;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$( echo &apos;ls -l | wc -l&apos; )</span>&quot;</span>
<span class="hljs-number">25</span>
</code></pre>
<p>&#xBA87; &#xAC00;&#xC9C0; &#xC608;&#xB97C; &#xB4E4;&#xC5B4;&#xBCF4;&#xBA74; &#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># if &#xB294; shell &#xD0A4;&#xC6CC;&#xB4DC;&#xB85C; &#xBA85;&#xB839;&#xCE58;&#xD658; &#xC774;&#xC804;&#xC5D0; &#xD574;&#xC11D;&#xC774; &#xC644;&#xB8CC;&#xB418;&#xBBC0;&#xB85C; &#xC774;&#xD6C4;&#xC5D0;&#xB294; &#xB2E8;&#xC21C; &#xC678;&#xBD80;&#xBA85;&#xB839;&#xC774; &#xB41C;&#xB2E4;.</span>
$ $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;if test 1 -eq 1; then echo equal; fi&quot;</span> )
<span class="hljs-keyword">if</span>: <span class="hljs-built_in">command</span> not found

<span class="hljs-comment"># &#xC774;&#xB54C; eval &#xC744; &#xC0AC;&#xC6A9;&#xD558;&#xBA74; &#xC815;&#xC0C1;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;&#xB429;&#xB2C8;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$( echo &quot;if test 1 -eq 1; then echo equal; fi&quot; )</span>&quot;</span>
equal
........................................................

<span class="hljs-comment"># &#xB9C8;&#xCC2C;&#xAC00;&#xC9C0;&#xB85C; &#xB300;&#xC785; &#xC5F0;&#xC0B0;&#xC740; &#xBA85;&#xB839;&#xCE58;&#xD658; &#xC774;&#xC804;&#xC5D0; &#xD574;&#xC11D;&#xC774; &#xC644;&#xB8CC;&#xB418;&#xBBC0;&#xB85C; &#xC774;&#xD6C4;&#xC5D0;&#xB294; &#xB2E8;&#xC21C; &#xC678;&#xBD80;&#xBA85;&#xB839;&#xC774; &#xB41C;&#xB2E4;.</span>
$ $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;AA=100&quot;</span> )
AA=<span class="hljs-number">100</span>: <span class="hljs-built_in">command</span> not found

$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$( echo &quot;AA=100&quot; )</span>&quot;</span>    <span class="hljs-comment"># eval &#xC744; &#xC0AC;&#xC6A9;&#xD558;&#xC5EC; &#xC815;&#xC0C1;&#xC801;&#xC73C;&#xB85C; &#xC2E4;&#xD589;</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$AA</span>
<span class="hljs-number">100</span>
.................................................................

<span class="hljs-comment"># &#xB2E4;&#xC74C;&#xC740; &#xBA85;&#xB839;&#xCE58;&#xD658; &#xACB0;&#xACFC;&#xB85C; export &#xBA85;&#xB839;&#xBB38;&#xC774; &#xCD9C;&#xB825;&#xB418;&#xBBC0;&#xB85C; &#xBB38;&#xC81C;&#xC5C6;&#xC774; &#xC2E4;&#xD589;&#xB420;&#xAC83; &#xAC19;&#xC9C0;&#xB9CC; &#xBA85;&#xB839;&#xBB38;&#xC5D0;</span>
<span class="hljs-comment"># &quot; &quot; quotes &#xC774; &#xC0AC;&#xC6A9;&#xB418;&#xC5B4; &#xBB38;&#xC81C;&#xAC00; &#xB429;&#xB2C8;&#xB2E4;. (quotes &#xD574;&#xC11D;&#xB3C4; &#xBA85;&#xB839;&#xCE58;&#xD658; &#xC774;&#xC804;&#xC5D0; &#xC644;&#xB8CC;&#xB429;&#xB2C8;&#xB2E4;.)</span>
$ <span class="hljs-built_in">echo</span> $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;export LESSCLOSE=&quot;/usr/bin/lesspipe %s %s&quot;&apos;</span> )
<span class="hljs-built_in">export</span> LESSCLOSE=<span class="hljs-string">&quot;/usr/bin/lesspipe %s %s&quot;</span>

$ $( <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;export LESSCLOSE=&quot;/usr/bin/lesspipe %s %s&quot;&apos;</span> )
bash: <span class="hljs-built_in">export</span>: <span class="hljs-string">&apos;%s&apos;</span>: not a valid identifier
bash: <span class="hljs-built_in">export</span>: <span class="hljs-string">&apos;%s&quot;&apos;</span>: not a valid identifier

$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$( echo &apos;export LESSCLOSE=&quot;/usr/bin/lesspipe %s %s&quot;&apos; )</span>&quot;</span>

$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$LESSCLOSE</span> 
/usr/bin/lesspipe %s %s
</code></pre>
<h3 id="eval-&#xBA85;&#xB839;&#xC758;-&#xC2E4;&#xD589;&#xB2E8;&#xACC4;">eval &#xBA85;&#xB839;&#xC758; &#xC2E4;&#xD589;&#xB2E8;&#xACC4;</h3>
<p>eval &#xBA85;&#xB839;&#xC740; &#xC8FC;&#xC5B4;&#xC9C4; &#xC778;&#xC218;&#xB4E4;&#xC744; &#xC77D;&#xC5B4; &#xB4E4;&#xC778; &#xD6C4; &#xC2E4;&#xD589;&#xD569;&#xB2C8;&#xB2E4;. &#xC5EC;&#xAE30;&#xC11C; &#xC8FC;&#xBAA9;&#xD574;&#xC57C; &#xB420; &#xC810;&#xC740; &#xB450; &#xB2E8;&#xACC4;&#xB97C; &#xAC70;&#xCCD0;&#xC11C; &#xC2E4;&#xD589;&#xC774; &#xB41C;&#xB2E4;&#xB294; &#xC810;&#xC785;&#xB2C8;&#xB2E4;. &#xCCAB;&#xC9F8;. &#xC77D;&#xC5B4;&#xB4E4;&#xC774;&#xB294; &#xB2E8;&#xACC4; , &#xB458;&#xC9F8;. &#xC2E4;&#xD589;&#xD558;&#xB294; &#xB2E8;&#xACC4;.  &#xADF8;&#xB798;&#xC11C; &#xACB0;&#xACFC;&#xC801;&#xC73C;&#xB85C; &#xC778;&#xC218;&#xBD80;&#xBD84;&#xC5D0;&#xC11C; &#xD655;&#xC7A5;&#xACFC; &#xCE58;&#xD658;&#xC774; &#xB450;&#xBC88; &#xC77C;&#xC5B4;&#xB098;&#xAC8C; &#xB429;&#xB2C8;&#xB2E4;. &#xC77D;&#xC5B4;&#xB4E4;&#xC77C; &#xB54C; &#xD55C;&#xBC88; &#xC2E4;&#xD589;&#xD560; &#xB54C; &#xD55C;&#xBC88;.</p>
<pre><code class="lang-bash">$ AA=<span class="hljs-number">100</span> BB=<span class="hljs-number">200</span>

<span class="hljs-comment"># &#xC778;&#xC218; &#xBD80;&#xBD84;&#xC5D0;&#xC11C; &#xD655;&#xC7A5;, &#xCE58;&#xD658;&#xC774; &#xC77C;&#xC5B4;&#xB098; $BB &#xAC00; 200 &#xC774;&#xB418;&#xACE0;</span>
<span class="hljs-comment"># &#xB9C8;&#xC9C0;&#xB9C9;&#xC5D0; &#xAC12;&#xC744; &#xD45C;&#xC2DC;&#xD558;&#xB294;&#xB370; &#xBD88;&#xD544;&#xC694;&#xD55C; quotes &#xC744; &#xC81C;&#xAC70;&#xD55C;&#xB2E4;.</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;$AA&apos;</span> <span class="hljs-variable">$BB</span>
<span class="hljs-variable">$AA</span> <span class="hljs-number">200</span>

<span class="hljs-comment"># 1. eval &#xC77D;&#xC5B4; &#xB4E4;&#xC774;&#xB294; &#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xC704;&#xC640; &#xAC19;&#xC774; &#xD655;&#xC7A5;, &#xCE58;&#xD658;&#xC774; &#xB418;&#xACE0; quotes &#xC774; &#xC0AD;&#xC81C;&#xB41C;&#xB2E4;.</span>
<span class="hljs-comment">#    echo $AA 200</span>
<span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4; &#xC5D0;&#xC11C;&#xB3C4; &#xD655;&#xC7A5;, &#xCE58;&#xD658;&#xC774; &#xC77C;&#xC5B4;&#xB098;&#xBBC0;&#xB85C; $AA &#xB294; 100 &#xC774;&#xB41C;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;$AA&apos;</span> <span class="hljs-variable">$BB</span>
<span class="hljs-number">100</span> <span class="hljs-number">200</span>

<span class="hljs-comment"># 1. single quotes &#xC774; escape &#xB410;&#xC73C;&#xBBC0;&#xB85C; read &#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xB0A8;&#xAC8C;&#xB41C;&#xB2E4;.</span>
<span class="hljs-comment">#    echo &apos;$AA&apos; 200</span>
<span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4; &#xC5D0;&#xC11C; quotes &#xC774; &#xC81C;&#xAC70;&#xB418;&#xC5B4; &#xD45C;&#xC2DC;&#xB41C;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> \<span class="hljs-string">&apos;&apos;</span><span class="hljs-variable">$AA</span><span class="hljs-string">&apos;\&apos;</span> <span class="hljs-variable">$BB</span>
<span class="hljs-variable">$AA</span> <span class="hljs-number">200</span>
</code></pre>
<p>brace &#xD655;&#xC7A5;&#xC5D0;&#xC11C;&#xB294; range &#xAC12;&#xC73C;&#xB85C; &#xBCC0;&#xC218;&#xB97C; &#xC0AC;&#xC6A9;&#xD558;&#xC9C0; &#xBABB;&#xD558;&#xB294;&#xB370; ( &#xBCC0;&#xC218;&#xD655;&#xC7A5;&#xC774; &#xB4A4;&#xC5D0; &#xC77C;&#xC5B4;&#xB098;&#xBBC0;&#xB85C; )<br>eval &#xBA85;&#xB839;&#xC744; &#xD65C;&#xC6A9;&#xD558;&#xBA74; brace &#xD655;&#xC7A5;&#xC5D0;&#xC11C;&#xB3C4; &#xBCC0;&#xC218;&#xB97C; &#xC0AC;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ a=<span class="hljs-number">1</span> b=<span class="hljs-number">5</span>

<span class="hljs-comment"># 1. eval &#xBA85;&#xB839; read &#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xBCC0;&#xC218;&#xD655;&#xC7A5;&#xC774; &#xC77C;&#xC5B4;&#xB09C;&#xB2E4;.</span>
<span class="hljs-comment">#    echo {1..5}</span>
<span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4; &#xC5D0;&#xC11C; brace &#xD655;&#xC7A5;&#xC774; &#xB41C;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> {<span class="hljs-variable">$a</span>..<span class="hljs-variable">$b</span>}
<span class="hljs-number">1</span> <span class="hljs-number">2</span> <span class="hljs-number">3</span> <span class="hljs-number">4</span> <span class="hljs-number">5</span>
</code></pre>
<p>&#xBA85;&#xB839;&#xC5D0; &#xC120;&#xD589;&#xD558;&#xB294; &#xB300;&#xC785; &#xC5F0;&#xC0B0;&#xC744; &#xC774;&#xC6A9;&#xD560; &#xB54C;&#xB3C4; eval &#xBA85;&#xB839;&#xC744; &#xC0AC;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.
&#xBA85;&#xB839; &#xC55E;&#xC5D0;&#xC11C; &#xB300;&#xC785;&#xD55C; &#xAC12;&#xC740; &#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xB420;&#xB54C; &#xD658;&#xACBD;&#xBCC0;&#xC218; &#xD615;&#xD0DC;&#xB85C; &#xC804;&#xB2EC;&#xB418;&#xC5B4; &#xC0AC;&#xC6A9;&#xB418;&#xBBC0;&#xB85C;
&#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xC774; &#xB3FC;&#xC57C; &#xC0AC;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xB294;&#xB370; &#xB2E4;&#xC74C;&#xC758; &#xACBD;&#xC6B0;&#xB294; echo &#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xB418;&#xAE30; &#xC804;&#xC5D0; 
<code>$A</code>, <code>$B</code>, <code>$C</code> &#xBCC0;&#xC218;&#xD655;&#xC7A5;&#xC774; &#xC77C;&#xC5B4;&#xB098;&#xBBC0;&#xB85C; &#xAE30;&#xC874;&#xC758; &#xAC12;&#xC744; &#xD45C;&#xC2DC;&#xD558;&#xAC8C; &#xB429;&#xB2C8;&#xB2E4;. </p>
<pre><code class="lang-bash">$ A=<span class="hljs-number">1</span> B=<span class="hljs-number">2</span> C=<span class="hljs-number">3</span>
$ A=<span class="hljs-number">4</span> B=<span class="hljs-number">5</span> C=<span class="hljs-number">6</span> <span class="hljs-built_in">echo</span> <span class="hljs-variable">$A</span> <span class="hljs-variable">$B</span> <span class="hljs-variable">$C</span>
<span class="hljs-number">1</span> <span class="hljs-number">2</span> <span class="hljs-number">3</span>                            
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$A</span> <span class="hljs-variable">$B</span> <span class="hljs-variable">$C</span>
<span class="hljs-number">1</span> <span class="hljs-number">2</span> <span class="hljs-number">3</span>
</code></pre>
<p>&#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; eval &#xBA85;&#xB839;&#xC744; &#xC0AC;&#xC6A9;&#xD558;&#xBA74; &#xD574;&#xACB0;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ A=<span class="hljs-number">1</span> B=<span class="hljs-number">2</span> C=<span class="hljs-number">3</span>

<span class="hljs-comment"># 1. eval &#xBA85;&#xB839; read &#xB2E8;&#xACC4;&#xC5D0; quotes &#xC774; &#xC0AD;&#xC81C;&#xB41C;&#xB2E4;.</span>
<span class="hljs-comment">#    echo $A $B $C</span>
<span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4; : &#xC774;&#xBBF8; eval &#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xC911;&#xC5D0; &#xC788;&#xC73C;&#xBBC0;&#xB85C; &#xB300;&#xC785;&#xD55C; &#xAC12;&#xC774; &#xC0AC;&#xC6A9;&#xB41C;&#xB2E4;.</span>
$ A=<span class="hljs-number">4</span> B=<span class="hljs-number">5</span> C=<span class="hljs-number">6</span> <span class="hljs-built_in">eval</span> <span class="hljs-string">&apos;echo $A $B $C&apos;</span>
<span class="hljs-number">4</span> <span class="hljs-number">5</span> <span class="hljs-number">6</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$A</span> <span class="hljs-variable">$B</span> <span class="hljs-variable">$C</span>      <span class="hljs-comment"># &#xBA85;&#xB839; &#xC885;&#xB8CC; &#xD6C4;&#xC5D0;&#xB294; &#xC6D0;&#xB798; &#xAC12;&#xC73C;&#xB85C; &#xBCF5;&#xADC0;</span>
<span class="hljs-number">1</span> <span class="hljs-number">2</span> <span class="hljs-number">3</span>                             

----------------------------------

$ arr=(foo bar zoo)

<span class="hljs-comment"># 1. eval &#xBA85;&#xB839; read &#xB2E8;&#xACC4;&#xC5D0; single quotes &#xC774; &#xC0AD;&#xC81C;&#xB41C;&#xB2E4;.</span>
<span class="hljs-comment">#    echo &quot;${arr[*]}&quot;</span>
<span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4; : &quot;${arr[*]}&quot; &#xAC00; double quote &#xB418;&#xC5B4;&#xC788;&#xC73C;&#xBBC0;&#xB85C; IFS=&apos;|&apos; &#xAC12;&#xC744; &#xAD6C;&#xBD84;&#xC790;&#xB85C; &#xCD9C;&#xB825;&#xB41C;&#xB2E4;.</span>
$ IFS=<span class="hljs-string">&apos;|&apos;</span> <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;&quot;${arr[*]}&quot;&apos;</span>
foo|bar|zoo
</code></pre>
<h4 id="printf-q-&#xB97C;-&#xC774;&#xC6A9;&#xD55C;-&#xC778;&#xC218;-&#xC124;&#xC815;">printf <code>%q</code> &#xB97C; &#xC774;&#xC6A9;&#xD55C; &#xC778;&#xC218; &#xC124;&#xC815;</h4>
<p>&#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; <code>printf %q</code> &#xB97C; &#xC774;&#xC6A9;&#xD55C; &#xC778;&#xC218; &#xC124;&#xC815;&#xC2DC;&#xC5D0;&#xB294; &#xB2E8;&#xC21C;&#xD788; set &#xBA85;&#xB839;&#xB9CC; 
&#xC0AC;&#xC6A9;&#xD558;&#xBA74; &#xC548;&#xB418;&#xACE0; eval set &#xC744; &#xC0AC;&#xC6A9;&#xD574;&#xC57C; &#xC778;&#xC218;&#xAC00; &#xC62C;&#xBC14;&#xB85C; &#xC124;&#xC815;&#xB429;&#xB2C8;&#xB2E4;.
<code>\</code> &#xBB38;&#xC790;&#xB97C; &#xC774;&#xC6A9;&#xD55C; escape sequences &#xCC98;&#xB9AC;&#xB3C4; &#xBCC0;&#xC218;&#xD655;&#xC7A5; &#xC804;&#xC5D0; &#xC644;&#xB8CC;&#xAC00; &#xB429;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># &quot;foo? bar *zoo[3]&quot; &#xC2A4;&#xD2B8;&#xB9C1;&#xC744; &#xD558;&#xB098;&#xC758; &#xC778;&#xC218;&#xB85C; &#xC124;&#xC815;&#xD558;&#xAE30; &#xC704;&#xD574; printf %q &#xC0AC;&#xC6A9;.</span>
$ arg=$( <span class="hljs-built_in">printf</span> <span class="hljs-string">&quot;%q&quot;</span> <span class="hljs-string">&quot;<span class="hljs-variable">$( echo -e &quot;foo? bar *zoo[3]&quot; )</span>&quot;</span> ) 
.............................................................

<span class="hljs-comment"># &#xB2E8;&#xC21C;&#xD788; set &#xBA85;&#xB839; &#xC0AC;&#xC6A9;                    # eval set &#xBA85;&#xB839; &#xC0AC;&#xC6A9;</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$arg</span>                            $ <span class="hljs-built_in">echo</span> <span class="hljs-built_in">set</span> -- <span class="hljs-variable">$arg</span>
foo\?\ bar\ \*zoo\[<span class="hljs-number">3</span>\]                 <span class="hljs-built_in">set</span> -- foo\?\ bar\ \*zoo\[<span class="hljs-number">3</span>\]

$ <span class="hljs-built_in">set</span> -- <span class="hljs-variable">$arg</span>                          $ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">set</span> -- <span class="hljs-variable">$arg</span>

$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$#</span>                              $ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$#</span>          <span class="hljs-comment"># &#xD558;&#xB098;&#xC758; &#xC778;&#xC218;&#xAC00; &#xB41C;&#xB2E4;.</span>
<span class="hljs-number">3</span>                                      <span class="hljs-number">1</span>

$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$1</span>&quot;</span>                            $ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$1</span>&quot;</span>
foo\?\                                 foo? bar *zoo[<span class="hljs-number">3</span>]

$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$3</span>&quot;</span>
\*zoo\[<span class="hljs-number">3</span>\]
</code></pre>
<h3 id="&#xC2A4;&#xD06C;&#xB9BD;&#xD2B8;-&#xC2E4;&#xD589;-&#xC911;&#xC5D0;-&#xBA85;&#xB839;&#xBB38;&#xC744;-&#xB9CC;&#xB4E4;&#xC5B4;-&#xC2E4;&#xD589;&#xD558;&#xAE30;">&#xC2A4;&#xD06C;&#xB9BD;&#xD2B8; &#xC2E4;&#xD589; &#xC911;&#xC5D0; &#xBA85;&#xB839;&#xBB38;&#xC744; &#xB9CC;&#xB4E4;&#xC5B4; &#xC2E4;&#xD589;&#xD558;&#xAE30;</h3>
<p><code>find . -name &quot;*.sh&quot;</code> &#xBA85;&#xB839;&#xBB38;&#xC744; &#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; &#xB9CC;&#xB4E4;&#xC5B4;&#xC11C; &#xC2E4;&#xD589;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ AA=<span class="hljs-string">&apos;find . -name&apos;</span>

$ BB=<span class="hljs-string">&apos;&quot;*.sh&quot;&apos;</span>

$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$AA</span> <span class="hljs-variable">$BB</span>&quot;</span>
./args.sh
./sub/foo.sh
./tmp/bar.sh
...
...
</code></pre>
<p>eval &#xBA85;&#xB839;&#xC744; &#xC0AC;&#xC6A9;&#xD558;&#xB2E4; &#xBCF4;&#xBA74; &#xBCF5;&#xC7A1;&#xD574; &#xBCF4;&#xC77C; &#xB54C;&#xAC00; &#xC788;&#xB294;&#xB370; &#xC774;&#xB54C;&#xB294; &#xC77D;&#xAE30; &#xBD80;&#xBD84;&#xC740; eval &#xC744; echo &#xB85C; &#xBC14;&#xAFB8;&#xC5B4; &#xC2E4;&#xD589;&#xD574; &#xBCF4;&#xBA74; &#xB429;&#xB2C8;&#xB2E4;.
echo &#xBA85;&#xB839;&#xC744; &#xC2E4;&#xD589;&#xD574;&#xC11C; &#xB098;&#xC628; &#xACB0;&#xACFC;&#xAC00; eval &#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xC2E4;&#xD589;&#xD558;&#xAC8C;&#xB420; &#xBA85;&#xB839;&#xC774; &#xB429;&#xB2C8;&#xB2E4;.
&#xADF8;&#xB9AC;&#xACE0; &#xADF8; &#xBA85;&#xB839;&#xC774; &#xC2E4;&#xD589;&#xB3FC;&#xC11C; &#xB098;&#xC628; &#xC885;&#xB8CC; &#xC0C1;&#xD0DC; &#xAC12;&#xC774; eval &#xBA85;&#xB839;&#xC758; &#xC885;&#xB8CC; &#xC0C1;&#xD0DC; &#xAC12;&#xC774; &#xB429;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$(echo hello world | sed &apos;s/hello/wc &lt;&lt;&lt; /&apos;)</span>&quot;</span>
<span class="hljs-number">1</span> <span class="hljs-number">1</span> <span class="hljs-number">6</span>
$ <span class="hljs-built_in">echo</span> $?
<span class="hljs-number">0</span>

<span class="hljs-comment"># 1. &#xC77D;&#xAE30;&#xB2E8;&#xACC4;: eval &#xC744; echo &#xB85C; &#xBCC0;&#xACBD;&#xD558;&#xC5EC; &#xC2E4;&#xD589;&#xD574;&#xBCF8;&#xB2E4;.</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$(echo hello world | sed &apos;s/hello/wc &lt;&lt;&lt; /&apos;)</span>&quot;</span>
wc &lt;&lt;&lt;  world    <span class="hljs-comment"># &#xC774; &#xBA85;&#xB839;&#xC774; eval &#xC774; &#xC2E4;&#xD589;&#xB2E8;&#xACC4;&#xC5D0;&#xC11C; &#xC2E4;&#xD589;&#xD558;&#xAC8C; &#xB420; &#xBA85;&#xB839;&#xC784;.</span>

$ wc &lt;&lt;&lt;  world  <span class="hljs-comment"># 2. &#xC2E4;&#xD589;&#xB2E8;&#xACC4;</span>
<span class="hljs-number">1</span> <span class="hljs-number">1</span> <span class="hljs-number">6</span>            <span class="hljs-comment"># &#xC774; &#xAC12;&#xC774; eval &#xBA85;&#xB839;&#xC758; stdout &#xAC12;&#xC774; &#xB418;&#xACE0;</span>
$ <span class="hljs-built_in">echo</span> $?
<span class="hljs-number">0</span>                <span class="hljs-comment"># &#xC774; &#xAC12;&#xC774; eval &#xBA85;&#xB839;&#xC758; &#xC885;&#xB8CC; &#xC0C1;&#xD0DC; &#xAC12;&#xC774; &#xB41C;&#xB2E4;.</span>
</code></pre>
<p>&#xB2E4;&#xC74C;&#xC740; <code>select</code> &#xBA85;&#xB839;&#xBB38;&#xC5D0;&#xC11C; &#xC0AC;&#xC6A9;&#xB418;&#xB294; <code>case</code> &#xBB38;&#xC744; eval &#xC744; &#xC0AC;&#xC6A9;&#xD574;&#xC11C; &#xB3D9;&#xC801;&#xC73C;&#xB85C; &#xC0DD;&#xC131;&#xD569;&#xB2C8;&#xB2E4;.<br>eval &#xC744; echo &#xB85C; &#xBCC0;&#xACBD;&#xD574;&#xC11C; &#xC2E4;&#xD589;&#xD574;&#xBCF4;&#xBA74; &#xC644;&#xC131;&#xB41C; case &#xBB38;&#xC744; &#xBCFC; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash"><span class="hljs-shebang">#!/bin/bash
</span>
PS3=$<span class="hljs-string">&apos;\n&gt;&gt;&gt; Select number: &apos;</span>

files=( `find /usr/bin -type f \( -name <span class="hljs-string">&apos;c??&apos;</span> -o -name <span class="hljs-string">&apos;d??&apos;</span> -o -name <span class="hljs-string">&apos;e??&apos;</span> \)` )

select pick <span class="hljs-keyword">in</span> <span class="hljs-string">&quot;<span class="hljs-variable">${files[@]}</span>&quot;</span>
<span class="hljs-keyword">do</span>
    <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$(
    echo &apos;case $pick in&apos;
    str=&quot;&quot;; for v in &quot;${files[@]}&quot;; do [[ ${v##*/} =~ ^c ]] &amp;&amp; str+=&quot;$v|&quot;; done
    echo &quot;${str%|})</span> char=c ;;&quot;</span>
    str=<span class="hljs-string">&quot;&quot;</span>; <span class="hljs-keyword">for</span> v <span class="hljs-keyword">in</span> <span class="hljs-string">&quot;<span class="hljs-variable">${files[@]}</span>&quot;</span>; <span class="hljs-keyword">do</span> [[ <span class="hljs-variable">${v##*/}</span> =~ ^d ]] &amp;&amp; str+=<span class="hljs-string">&quot;<span class="hljs-variable">$v</span>|&quot;</span>; <span class="hljs-keyword">done</span>
    <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">${str%|}</span>) char=d ;;&quot;</span>
    str=<span class="hljs-string">&quot;&quot;</span>; <span class="hljs-keyword">for</span> v <span class="hljs-keyword">in</span> <span class="hljs-string">&quot;<span class="hljs-variable">${files[@]}</span>&quot;</span>; <span class="hljs-keyword">do</span> [[ <span class="hljs-variable">${v##*/}</span> =~ ^e ]] &amp;&amp; str+=<span class="hljs-string">&quot;<span class="hljs-variable">$v</span>|&quot;</span>; <span class="hljs-keyword">done</span>
    <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">${str%|}</span>) char=e ;;&quot;</span>
    <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;esac&apos;</span>
    )<span class="hljs-string">&quot;
    echo
    echo &quot;</span>\<span class="hljs-string">&quot;<span class="hljs-variable">$pick</span>\&quot; command starts with \&quot;<span class="hljs-variable">$char</span>\&quot;.&quot;</span>
    <span class="hljs-built_in">echo</span>
    <span class="hljs-built_in">break</span>
<span class="hljs-keyword">done</span>

----------------------------------------------------------------------

$ ./test.sh
<span class="hljs-number">1</span>) /usr/bin/eog    <span class="hljs-number">4</span>) /usr/bin/cmp   <span class="hljs-number">7</span>) /usr/bin/col  <span class="hljs-number">10</span>) /usr/bin/cvt
<span class="hljs-number">2</span>) /usr/bin/dir    <span class="hljs-number">5</span>) /usr/bin/cut   <span class="hljs-number">8</span>) /usr/bin/env  <span class="hljs-number">11</span>) /usr/bin/ctr
<span class="hljs-number">3</span>) /usr/bin/cat    <span class="hljs-number">6</span>) /usr/bin/dig   <span class="hljs-number">9</span>) /usr/bin/eqn

&gt;&gt;&gt; Select number: <span class="hljs-number">3</span>

<span class="hljs-string">&quot;/usr/bin/cat&quot;</span> <span class="hljs-built_in">command</span> starts with <span class="hljs-string">&quot;c&quot;</span>.
</code></pre>
<p>&#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; &#xD568;&#xC218;&#xB97C; &#xB3D9;&#xC801;&#xC73C;&#xB85C; &#xB9CC;&#xB4E4;&#xC5B4; &#xC2E4;&#xD589;&#xD558;&#xB294; &#xAC83;&#xB3C4; &#xAC00;&#xB2A5;&#xD569;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ <span class="hljs-function"><span class="hljs-title">main</span></span>() {
&gt;     <span class="hljs-built_in">local</span> fbody=<span class="hljs-string">&apos;() { echo &quot;function name is : $FUNCNAME&quot;; }&apos;</span>
&gt;     <span class="hljs-built_in">local</span> fname
&gt;     <span class="hljs-keyword">for</span> fname <span class="hljs-keyword">in</span> foo{<span class="hljs-number">1</span>..<span class="hljs-number">10</span>}; <span class="hljs-keyword">do</span>
&gt;         <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">${fname}</span><span class="hljs-variable">${fbody}</span>&quot;</span>   <span class="hljs-comment"># &#xC774; &#xBD80;&#xBD84;&#xC5D0;&#xC11C; &#xD568;&#xC218; &#xC815;&#xC758;&#xAC00; &#xB428;</span>
&gt;         <span class="hljs-variable">$fname</span>                    <span class="hljs-comment"># &#xD568;&#xC218;&#xBA85;&#xC73C;&#xB85C; &#xC2E4;&#xD589;</span>
&gt;     <span class="hljs-keyword">done</span>
&gt; }

$ main
<span class="hljs-keyword">function</span> name is : foo1
<span class="hljs-keyword">function</span> name is : foo2
<span class="hljs-keyword">function</span> name is : foo3
...
...
</code></pre>
<pre><code class="lang-bash"><span class="hljs-keyword">if</span> <span class="hljs-built_in">test</span> yes = <span class="hljs-string">&quot;<span class="hljs-variable">$_G_HAVE_XSI_OPS</span>&quot;</span>; <span class="hljs-keyword">then</span>
  _d=<span class="hljs-string">&apos;case $1 in
        */*) func_dirname_result=${1%/*}$2 ;;
        *  ) func_dirname_result=$3        ;;
      esac&apos;</span>
<span class="hljs-keyword">else</span>
  _d=<span class="hljs-string">&apos;func_dirname_result=`$ECHO &quot;$1&quot; | $SED &quot;$sed_dirname&quot;`
      if test &quot;X$func_dirname_result&quot; = &quot;X$1&quot;; then
        func_dirname_result=$3
      else
        func_append func_dirname_result &quot;$2&quot;
      fi&apos;</span>
<span class="hljs-keyword">fi</span>

<span class="hljs-built_in">eval</span> <span class="hljs-string">&apos;func_dirname ()
{
    $debug_cmd

    &apos;</span><span class="hljs-string">&quot;<span class="hljs-variable">$_d</span>&quot;</span><span class="hljs-string">&apos;
}&apos;</span>
</code></pre>
<h3 id="eval-&#xBA85;&#xB839;&#xC744;-&#xC774;&#xC6A9;&#xD55C;-indirection">eval &#xBA85;&#xB839;&#xC744; &#xC774;&#xC6A9;&#xD55C; indirection</h3>
<p>&#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; eval &#xBA85;&#xB839;&#xC744; indirection &#xC5D0; &#xD65C;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ AA=BB                        $ hello=<span class="hljs-number">123</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$AA</span>                     $ linux=hello
BB                             $ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> \$<span class="hljs-variable">$linux</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-variable">$AA</span>=<span class="hljs-number">100</span>                 <span class="hljs-number">123</span>
$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$BB</span>
<span class="hljs-number">100</span>                            <span class="hljs-keyword">if</span> <span class="hljs-built_in">test</span> <span class="hljs-variable">$hello</span> <span class="hljs-operator">-eq</span> $(<span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> \$<span class="hljs-variable">$linux</span>); <span class="hljs-keyword">then</span>
                                   . . .
                               <span class="hljs-keyword">fi</span>
</code></pre>
<p>&#xB300;&#xC785;&#xC5F0;&#xC0B0;&#xC740; shell keyword &#xC640; &#xAC19;&#xC774; &#xBCC0;&#xC218;&#xD655;&#xC7A5; &#xC804;&#xC5D0; &#xCC98;&#xB9AC;&#xB418;&#xBBC0;&#xB85C; &#xB2E8;&#xC21C;&#xD788; <code>$AA=100</code> &#xB85C; &#xD560; &#xC218; &#xC5C6;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ AA=BB

$ <span class="hljs-variable">$AA</span>=<span class="hljs-number">100</span>
BB=<span class="hljs-number">100</span>: <span class="hljs-built_in">command</span> not found
</code></pre>
<p>&#xB2E4;&#xC74C;&#xC740; indirection &#xC744; &#xD65C;&#xC6A9;&#xD558;&#xC5EC; &#xB9C8;&#xC9C0;&#xB9C9; &#xC778;&#xC218; &#xAC12;&#xC744; file &#xBCC0;&#xC218;&#xC5D0; &#xB300;&#xC785;&#xD569;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ cat test.sh                                 <span class="hljs-function"><span class="hljs-title">foo</span></span> () {
<span class="hljs-comment">#!/bin/sh                                         eval $1=&apos;$(echo $&apos;$2&apos;)&apos;</span>
                                                  <span class="hljs-comment"># &#xB610;&#xB294; eval $1=&apos;${!2}&apos;</span>
<span class="hljs-built_in">eval</span> file=<span class="hljs-string">&apos;$&apos;</span><span class="hljs-variable">$#</span>                               }

<span class="hljs-built_in">echo</span> file name : <span class="hljs-string">&quot;<span class="hljs-variable">$file</span>&quot;</span>                      $ aaa=<span class="hljs-number">100</span> bbb=<span class="hljs-number">200</span>
--------------------------                    
                                              $ foo aaa bbb
$ ./test.sh <span class="hljs-operator">-a</span> -b -c data.txt                    
file name : data.txt                          $ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$aaa</span>
                                              <span class="hljs-number">200</span>
</code></pre>
<h3 id="&#xD30C;&#xC774;&#xD504;-&#xC640;-redirection">&#xD30C;&#xC774;&#xD504; &#xC640; redirection</h3>
<p>eval &#xC740; &#xBA85;&#xB839;&#xC774;&#xAE30; &#xB54C;&#xBB38;&#xC5D0; &#xD30C;&#xC774;&#xD504;&#xC640; &#xAC19;&#xC774; &#xC0AC;&#xC6A9;&#xB420; &#xACBD;&#xC6B0; &#xD55C;&#xCABD;&#xC5D0;&#xB9CC; &#xC801;&#xC6A9;&#xB418;&#xB294; &#xAC83;&#xC785;&#xB2C8;&#xB2E4;.<br>&#xADF8;&#xB7EC;&#xBBC0;&#xB85C; &#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC740; &#xACBD;&#xC6B0; eval &#xC740; &#xD30C;&#xC774;&#xD504; &#xC67C;&#xCABD;&#xC5D0; &#xC704;&#xCE58;&#xD55C; &#xBA85;&#xB839;&#xC5D0;&#xB9CC; &#xC801;&#xC6A9;&#xB429;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># command1 &#xC5D0;&#xB9CC; eval &#xC774; &#xC801;&#xC6A9;</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">command</span>1 ... | <span class="hljs-built_in">command</span>2 ...
</code></pre>
<p>&#xC804;&#xCCB4; &#xBA85;&#xB839;&#xC744; eval &#xD558;&#xB824;&#xBA74; &#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774;&#xD569;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># command2 &#xC5D0;&#xB3C4; eval &#xC774; &#xC801;&#xC6A9;&#xB418;&#xB824;&#xBA74;</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">command</span>1 ... | <span class="hljs-built_in">eval</span> <span class="hljs-built_in">command</span>2 ...

<span class="hljs-comment"># &#xC804;&#xCCB4; &#xBA85;&#xB839;&#xC744; quote &#xD558;&#xBA74; &#xD558;&#xB098;&#xC758; eval &#xB9CC; &#xC0AC;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;command1 ... | command2 ...&quot;</span>

<span class="hljs-comment"># &#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; &#xD30C;&#xC774;&#xD504;&#xB97C; escape &#xD560; &#xC218;&#xB3C4; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">command</span>1 ... \| <span class="hljs-built_in">command</span>2 ...

<span class="hljs-comment"># &#xD30C;&#xC774;&#xD504;&#xB97C; escape &#xD560; &#xACBD;&#xC6B0; redirection &#xC774; &#xC0AC;&#xC6A9;&#xB418;&#xBA74; &#xAC19;&#xC774; escape &#xD574;&#xC918;&#xC57C; &#xD569;&#xB2C8;&#xB2E4;.</span>
$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">command</span>1  ... <span class="hljs-string">&apos;2&gt;&amp;1 |&apos;</span> <span class="hljs-built_in">command</span>2 ...
</code></pre>
<h3 id="ifs-&#xC640;-eval">$IFS &#xC640; eval</h3>
<pre><code class="lang-sh">$ cmd=<span class="hljs-string">&apos;echo hello eval&apos;</span>

$ <span class="hljs-variable">$cmd</span>              <span class="hljs-comment"># &#xB2E8;&#xC5B4;&#xBD84;&#xB9AC;&#xC5D0; &#xC758;&#xD574; echo &#xB294; &#xBA85;&#xB839; hello eval &#xC740; &#xC778;&#xC218;&#xAC00; &#xB41C;&#xB2E4;.</span>
hello <span class="hljs-built_in">eval</span>

$ IFS=$<span class="hljs-string">&apos;\n&apos;</span>         <span class="hljs-comment"># IFS &#xAC12;&#xC744; newline &#xC73C;&#xB85C; &#xBCC0;&#xACBD;&#xD558;&#xBA74;</span>

$ <span class="hljs-variable">$cmd</span>              <span class="hljs-comment"># &#xB2E8;&#xC5B4;&#xBD84;&#xB9AC;&#xAC00; &#xC77C;&#xC5B4;&#xB098;&#xC9C0; &#xC54A;&#xC544; &apos;echo hello eval&apos; &#xC804;&#xCCB4;&#xAC00; &#xD558;&#xB098;&#xC758; &#xBA85;&#xB839;&#xC774; &#xB41C;&#xB2E4;.</span>
<span class="hljs-built_in">echo</span> hello <span class="hljs-built_in">eval</span>: <span class="hljs-built_in">command</span> not found

$ <span class="hljs-built_in">eval</span> <span class="hljs-variable">$cmd</span>         <span class="hljs-comment"># &#xC774;&#xB54C; eval &#xC744; &#xC0AC;&#xC6A9;&#xD558;&#xBA74; &#xC2E4;&#xD589;&#xC774; &#xB41C;&#xB2E4;.</span>
hello <span class="hljs-built_in">eval</span>
</code></pre>
<h3 id="quotes-&#xACFC;-eval">quotes &#xACFC; eval</h3>
<pre><code class="lang-sh">$ foo=<span class="hljs-string">&apos;&quot;hello         eval&quot;&apos;</span>     <span class="hljs-comment"># foo &#xBCC0;&#xC218;&#xAC12;&#xC5D0; &#xACF5;&#xBC31;&#xACFC; quotes &#xC774; &#xD3EC;&#xD568;&#xB428;</span>

$ <span class="hljs-built_in">echo</span> <span class="hljs-variable">$foo</span>
<span class="hljs-string">&quot;hello eval&quot;</span>

$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$foo</span>&quot;</span>
<span class="hljs-string">&quot;hello         eval&quot;</span>

$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;$foo&apos;</span>         <span class="hljs-comment"># single quotes &#xC740; &#xBCC0;&#xC218;&#xAC12;&#xC5D0;&#xC11C; quotes &#xC744; &#xC720;&#xC9C0;&#xD558;&#xB294; &#xC5ED;&#xD560;&#xC744; &#xD55C;&#xB2E4;.</span>
<span class="hljs-string">&quot;hello eval&quot;</span>

$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$foo</span>&quot;</span>         <span class="hljs-comment"># &#xBCC0;&#xC218;&#xAC12;&#xC5D0;&#xC11C; double quotes &#xC774; &#xC81C;&#xAC70;&#xB428;.</span>
hello         <span class="hljs-built_in">eval</span>

$ <span class="hljs-built_in">eval</span> <span class="hljs-built_in">echo</span> <span class="hljs-string">&apos;&quot;$foo&quot;&apos;</span>       <span class="hljs-comment"># double quotes &#xC740; &#xBCC0;&#xC218;&#xAC12;&#xC5D0;&#xC11C; &#xACF5;&#xBC31;&#xC744; &#xC720;&#xC9C0;&#xD558;&#xB294; &#xC5ED;&#xD560;&#xC744; &#xD55C;&#xB2E4;.</span>
<span class="hljs-string">&quot;hello         eval&quot;</span>
</code></pre>
<h1 id="quiz">Quiz</h1>
<p>single quotes, double quotes &#xC774; &#xBAA8;&#xB450; &#xD3EC;&#xD568;&#xB41C; &#xBA85;&#xB839;&#xBB38;&#xC744; &#xBCC0;&#xC218;&#xC5D0; &#xB300;&#xC785;&#xD574;&#xC11C;
eval &#xC744; &#xC774;&#xC6A9;&#xD574; &#xC2E4;&#xD589;&#xD558;&#xB824;&#xACE0; &#xD569;&#xB2C8;&#xB2E4;.
&#xC774;&#xB54C;&#xB294; &#xBCC0;&#xC218;&#xC5D0; &#xB300;&#xC785;&#xD560; &#xB54C; quotes &#xC744; escape &#xD558;&#xB294; &#xAC8C; &#xBCF5;&#xC7A1;&#xD574;&#xC9C8; &#xC218; &#xC788;&#xB294;&#xB370;&#xC694;.
quotes &#xC744; &#xB530;&#xB85C; escape &#xD560; &#xD544;&#xC694; &#xC5C6;&#xC774; &#xADF8;&#xB300;&#xB85C; &#xBCC0;&#xC218;&#xC5D0; &#xB300;&#xC785;&#xD558;&#xB824;&#xBA74; &#xC5B4;&#xB5BB;&#xAC8C; &#xD560;&#xAE4C;&#xC694;?</p>
<p>&#xB2E4;&#xC74C;&#xACFC; &#xAC19;&#xC774; <a href="here_document.html">here document</a> &#xB97C; &#xD65C;&#xC6A9;&#xD558;&#xBA74;
&#xD504;&#xB86C;&#xD504;&#xD2B8;&#xC5D0;&#xC11C; &#xC2E4;&#xD589;&#xD55C; &#xBA85;&#xB839;&#xBB38; &#xADF8;&#xB300;&#xB85C; &#xBCC0;&#xC218;&#xC5D0; &#xB300;&#xC785;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;.</p>
<pre><code class="lang-bash">$ find * -name <span class="hljs-string">&apos;Packages*&apos;</span> -type f -exec \
    sh -c <span class="hljs-string">&apos;echo $(md5sum &quot;{}&quot; | awk &apos;</span>\<span class="hljs-string">&apos;&apos;</span>{<span class="hljs-built_in">print</span> <span class="hljs-variable">$1</span>}<span class="hljs-string">&apos;\&apos;</span><span class="hljs-string">&apos;) $(stat -c %s &quot;{}&quot;) &quot;{}&quot;&apos;</span> \;

b49dd0f63bca9b3a139c5af3dd94c816 <span class="hljs-number">380</span> Packages
e805c26ff46c6e138e3<span class="hljs-built_in">cd</span>198cff281ea <span class="hljs-number">301</span> Packages.bz2
<span class="hljs-number">997</span>a7252f202566a1e5fdc5b50c2ffdf <span class="hljs-number">283</span> Packages.gz

-------------------------------------------------

$ <span class="hljs-built_in">read</span> -rd <span class="hljs-string">&apos;&apos;</span> CMD1 &lt;&lt;\EOF || :
find * -name <span class="hljs-string">&apos;Packages*&apos;</span> -type f -exec \
EOF

$ <span class="hljs-built_in">read</span> -rd <span class="hljs-string">&apos;&apos;</span> CMD2 &lt;&lt;\EOF || :
sh -c <span class="hljs-string">&apos;echo $(md5sum &quot;{}&quot; | awk &apos;</span>\<span class="hljs-string">&apos;&apos;</span>{<span class="hljs-built_in">print</span> <span class="hljs-variable">$1</span>}<span class="hljs-string">&apos;\&apos;</span><span class="hljs-string">&apos;) $(stat -c %s &quot;{}&quot;) &quot;{}&quot;&apos;</span> \;
EOF

$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$CMD1</span><span class="hljs-variable">$CMD2</span>&quot;</span>
find * -name <span class="hljs-string">&apos;Packages*&apos;</span> -type f -exec \
sh -c <span class="hljs-string">&apos;echo $(md5sum &quot;{}&quot; | awk &apos;</span>\<span class="hljs-string">&apos;&apos;</span>{<span class="hljs-built_in">print</span> <span class="hljs-variable">$1</span>}<span class="hljs-string">&apos;\&apos;</span><span class="hljs-string">&apos;) $(stat -c %s &quot;{}&quot;) &quot;{}&quot;&apos;</span> \;

$ <span class="hljs-built_in">eval</span> <span class="hljs-string">&quot;<span class="hljs-variable">$CMD1</span><span class="hljs-variable">$CMD2</span>&quot;</span>
b49dd0f63bca9b3a139c5af3dd94c816 <span class="hljs-number">380</span> Packages
e805c26ff46c6e138e3<span class="hljs-built_in">cd</span>198cff281ea <span class="hljs-number">301</span> Packages.bz2
<span class="hljs-number">997</span>a7252f202566a1e5fdc5b50c2ffdf <span class="hljs-number">283</span> Packages.gz

---------------------------------------------------  &#xB610;&#xB294;

$ CMD=$( cat &lt;&lt;\EOF
find * -name <span class="hljs-string">&apos;Packages*&apos;</span> -type f -exec \
EOF
)$<span class="hljs-string">&apos;\n&apos;</span>

$ CMD+=$( cat &lt;&lt;\EOF
sh -c <span class="hljs-string">&apos;echo $(md5sum &quot;{}&quot; | awk &apos;</span>\<span class="hljs-string">&apos;&apos;</span>{<span class="hljs-built_in">print</span> <span class="hljs-variable">$1</span>}<span class="hljs-string">&apos;\&apos;</span><span class="hljs-string">&apos;) $(stat -c %s &quot;{}&quot;) &quot;{}&quot;&apos;</span> \;
EOF
)

$ <span class="hljs-built_in">echo</span> <span class="hljs-string">&quot;<span class="hljs-variable">$CMD</span>&quot;</span>
find * -name <span class="hljs-string">&apos;Packages*&apos;</span> -type f -exec \
sh -c <span class="hljs-string">&apos;echo $(md5sum &quot;{}&quot; | awk &apos;</span>\<span class="hljs-string">&apos;&apos;</span>{<span class="hljs-built_in">print</span> <span class="hljs-variable">$1</span>}<span class="hljs-string">&apos;\&apos;</span><span class="hljs-string">&apos;) $(stat -c %s &quot;{}&quot;) &quot;{}&quot;&apos;</span> \;
</code></pre>

                    
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