shell_script.md

Shell Script

Commands

List the nth line of a file

1.  head -n ${n} file | tail -n 1
2.  sed '${n}p;d' file
3.  sed -n '${n}p' file
4.  awk 'NR==${n}{print;exit}' file

List from line m to line n

1.  head -n ${n} file | tail -n ${$($n-$m)}
2.  sed '${m},${n}p;d' file
3.  sed -n '${m},${n}p' file
4.  awk 'NR>=${m}&&NR<=${n}{print;exit}' file

Word Frequency

Description

cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -n -r | awk '{print $2" "$1}'

Validate Phone Numbers

Description

grep -P '^(\(\d{3}\)\s|\d{3}-)\d{3}-\d{4}$' file.txt

Execute Command Without Output

Redirect output(stdout) to /dev/null.

If we also want to ignore err, we need to redirect stderr as well by using 2>&1.

Eventually, we have

$ <command> > /dev/null 2>&1