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

Answer 1

I would suggest:

#!/bin/bash

s1="hi"
s2="hi"

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

Without the double quotes and with only one equals.

Answer 2

This question has already great answers, but here it appears that there is a slight confusion between using single equal and double equals in

if [ "$s1" == "$s2" ]

The main difference lies in which scripting language you are using. If you are using Bash then include #!/bin/bash in the starting of the script and save your script as filename.bash. To execute, use bash filename.bash - then you have to use ==.

If you are using sh then use #!/bin/sh and save your script as filename.sh. To execute use sh filename.sh - then you have to use single =. Avoid intermixing them.

Answer 3

For string equality comparison, use:

if [[ "$s1" == "$s2" ]]

For string does NOT equal comparison, use:

if [[ "$s1" != "$s2" ]]

For the a contains b, use:

if [[ $s1 == *"$s2"* ]]

(and make sure to add spaces between the symbols):

Bad:

if [["$s1" == "$s2"]]

Good:

if [[ "$s1" == "$s2" ]]

Answer 4

You need spaces:

if [ "$s1" == "$s2" ]

Answer 5

This is more a clarification than an answer! Yes, the clue is in the error message:

[hi: command not found

which shows you that your "hi" has been concatenated to the "[".

Unlike in more traditional programming languages, in Bash, "[" is a command just like the more obvious "ls", etc. - it's not treated specially just because it's a symbol, hence the "[" and the (substituted) "$s1" which are immediately next to each other in your question, are joined (as is correct for Bash), and it then tries to find a command in that position: [hi - which is unknown to Bash.

In C and some other languages, the "[" would be seen as a different "character class" and would be disjoint from the following "hi".

Hence you require a space after the opening "[".

Answer 6

I suggest this one:

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

Notice the white space between the openning/closing brackets and the variables and also the white spaces wrapping the '=' sign.

Also, be careful of your script header. It's not the same thing whether you use

#!/bin/bash

or

#!/bin/sh

Here's the source.