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by Qadeer Ahmad Khan

Shell (unix) commands you always forget

This is a list of typical commands that I often have to Google because I forget either their usage or important flags.

Using grep with perl type regex

ls | grep -P "dirNo\d\d$"

Using the -P flag lets you search for more advanced regex expressions. Other useful grep flags:

  • -i ignore case
  • -o print only matching
  • -v invert matching
  • -A number show lines after match
  • -B number show lines before match

Using grep without pipe

grep "hell\w" . -R

searches after pattern hell\w in current directory and sub-directories. Add -h to ignore filenames in output.

For loops - range

for ((i = 1; i<=10; i++)); do echo $i; done

For loops - command

for v in `ls`; do echo $v; done

Bash script for traversing arguments and line breaks


SENTENCES="line 1${IFS}line2${IFS}line3"

for arg in "$@" # for all input arguments
 #automatically loops through line breaks duo to IFS value
   for s in $SENTENCES
       echo "$arg=$s"

Simple sed commands

Search and replace file content:

sed -i "s/<searchpattern>/<replace>/g" <files>

From pipe and print result:

sed -n "s/<searchpattern>/<replace>/p"

To replace matched regex groups, use \1, \2 and so on.

Finding size of subfolders, sorted.

du -h -d 1 | sort -hr
  • du -h d -1 is the disc usage command with the -h flag for outputting human readable sizes and -d 1 for depth of 1 sub dirs.
  • sort -hr sorts human readable sizes in reverse order.