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cheatsheet.md

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[[TOC]]

Generating (config) files dynamically based on environemnts

cat > myfile <<ANY
any content of file with arbitrary
$ENVVAR replacements
ANY

create a file myfile with the content between the ANY delimiters and all envs replaced.

Make sure script can be executed from any directory

Get script directory and cd into it

DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
cd $DIR

Select specific line from file

cat file | sed -n ${LINE}','${LINE}'p'

where $LINE is the line number you want to extract.

Read what is passed on stdin into variable

function getinput {
  while read line
  do
    echo -e "$line"
  done
}
X=$(getinput)

Debug/Trace script/section line by line

set -x
# Debug On
set +x
# Debug Off

Do arithemtic with arbitrary precision

echo "scale=$SCALE; 1.5/0.33" | bc

where $SCALE denotes the precision in decimals. scale=0 is useful to return integer values (floor). bc also handles boolean results as 0 false and 1 true.

echo "10.3 > 10.2" | bc

Loop given number of steps

for i in `seq 1 $n`; do
  echo $i
done

loop $n times.

Find content in files in directory structure

grep "$TOFIND" `find . -name "*.*"`

find and report all files in current directory and sub directories with . in their filename and the contents in $TOFIND.

Count occurances of content in file column

cat file | awk {'print $'$COL'} | sort | uniq -c

count occurancoes of different content in columen $COL in file file.

Average and standard deviation of column one-liners

AVG=`cat file | awk '{ sum += $'$COL'; n++ } END { if (n > 0) print sum / n; }'`
STD=`cat file | awk '{sum += $'$COL'; sum2 += ($'$COL')^2} END {printf "%f \n", sqrt((sum2-sum^2/NR)/NR)}`

Compute average and standard deviation of column $COL in file file.

Count rows and columns in file

COLUMNS=`head -n 1 file | awk '{print NF}'`
ROWS=`cat file | wc -l`

count columns and rows in file file.

Use default values if envs are not set

VAL=${VAL:-10}

Sets default value 10 to env VAL if it is not set.

Launch process in background then kill in another script

Launch

nohup ./process.sh > process.log 2>&1 &
echo -n "$!" > process.pid

Stop

cat process.pid | xargs kill