How do I compare two string variables in an if statement in Bash

Question

I m trying to get an if statement to work in Bash  using Ubuntu       bin bash  s1  hi  s2  hi   if    s1       s2   then   echo match fi   I ve tried various forms of the if statement  using     s1       s2     with and without quotes  using       and -eq  but I still get the following error       hi  command not found   I ve looked at various sites and tutorials and copied those  but it doesn t work - what am I doing wrong   Eventually  I want to say if  s1 contains  s2  so how can I do that   I did just work out the spaces bit       How do I say contains   I tried  if      s1        s2        but it didn t work

User · Answer

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.

User · Answer

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

User · Answer

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

User · Answer

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    quot  s1 quot      quot  s2 quot     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

User · Answer

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

User · Answer

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     amp  amp  echo match

User · Answer

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

User · Answer

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

User · Answer

if     s1       s2     then echo match  fi match   test  s1     s2   echo match match

User · Answer

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

User · Answer

You need spaces   if     s1       s2

User · Answer

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

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

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