Command Line Bash

Examples of using Bash on the command line

Compare two unsorted lists

# Looks for all lines in `second-file.txt`, which don't match
# any line in `first-file.txt`.
grep -Fxv -f first-file.txt second-file.txt

Loop over an array of ints

for i in {1,2,3}; do echo ${i}; done

for i in {1,2,3}; do echo "$i"; done

Loop over a range of ints

for i in {1..10}; do echo ${i}; done

for i in {1..10}; do echo "$i"; done

Loop over an array of strings

for s in a b c d e; do echo "$s"; done

Run the last command with substituion

Substitute the first occurence

^foo^bar

Substitute all occurences

!!:gs/foo/bar/
#
# !! - reruns the last command. You can also use !-2 to run two commands ago, !echo to run the last command that starts with echo
#
# :gs says to do a global (all instances) search/replace. If you wanted to just do replace the first instance, you would use ':s'
#
# Finally, /foo/bar/ says to replace foo with bar

Run command on an interval

Every 1 seconds

while sleep 1; do [cmd]; done

while sleep 1; do echo "Hello"; echo "World"; done

while true; do clear; ./runScript.sh; sleep 1; done

Every 1 milliseconds

while sleep 0.1; do [cmd]; done

while sleep 0.1; do echo "Hello"; done

Run command on interval with incrementing variable

Every 1 seconds

i=1; while true; do echo "out - $i"; ((i++)); sleep 1; done

While loop with a multi-line string

Use a Here String to effectively create a for loop with multiline data

while read i
do
  echo "test$i"
done <<< 'a
b
c'

AWK

Print the 5th column

echo "This is a string made of columns" | awk '{print $5}'

Print the 5th column, with quotation marks, using printf

echo "This is a string made of columns" | awk '{printf("\"%s\"", $5);}'

Print all columns after, and including, the 5th column

echo "This is a string made of columns" | awk '{ s = ""; for (i = 5; i <= NF; i++) s = s $i " "; print s }'

Change the field seperator

echo "This\is\a\string\with\a\different\seperator" | awk -F'\' '{print $4}'

Pad filename with zeros

Change spaces to "-" and pad the number at the end with 4 zeros

echo "This is a file name 3" | awk '{printf "%s-%s-%s-%s-%s-%05d", $1, $2, $3, $4, $5, $6}'

Grep

Command	Description
make run | grep --line-buffered -i "thing1\|thing2"	Grep a stream of data for thing1 or thing2, case-insensitively