How do I compare two string variables in an 'if' statement in Bash? [duplicate]

Answer 1

Use:

#!/bin/bash

s1="hi"
s2="hi"

if [ "x$s1" == "x$s2" ]
then
  echo match
fi

Adding an additional string inside makes it more safe.

You could also use another notation for single-line commands:

[ "x$s1" == "x$s2" ] && echo match

Answer 2

For a version with pure Bash and without test, but really ugly, try:

if ( exit "${s1/*$s2*/0}" )2>/dev/null
then
   echo match
fi

Explanation: In ( )an extra subshell is opened. It exits with 0 if there was a match, and it tries to exit with $s1 if there was no match which raises an error (ugly). This error is directed to /dev/null.

Answer 3

I don't have access to a Linux box right now, but [ is actually a program (and a Bash builtin), so I think you have to put a space between [ and the first parameter.

Also note that the string equality operator seems to be a single =.

Answer 4

$ if [ "$s1" == "$s2" ]; then echo match; fi
match
$ test "s1" = "s2" ;echo match
match
$

Answer 5

Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash IMO.

Here are some examples Bash 4+:

Example 1, check for 'yes' in string (case insensitive):

if [[ "${str,,}" == *"yes"* ]] ;then

Example 2, check for 'yes' in string (case insensitive):

if [[ "$(echo "$str" | tr '[:upper:]' '[:lower:]')" == *"yes"* ]] ;then

Example 3, check for 'yes' in string (case sensitive):

 if [[ "${str}" == *"yes"* ]] ;then

Example 4, check for 'yes' in string (case sensitive):

 if [[ "${str}" =~ "yes" ]] ;then

Example 5, exact match (case sensitive):

 if [[ "${str}" == "yes" ]] ;then

Example 6, exact match (case insensitive):

 if [[ "${str,,}" == "yes" ]] ;then

Example 7, exact match:

 if [ "$a" = "$b" ] ;then

Answer 6

You should be careful to leave a space between the sign of '[' and double quotes where the variable contains this:

if [ "$s1" == "$s2" ]; then
#   ^     ^  ^     ^
   echo match
fi

The ^s show the blank spaces you need to leave.