Use Awk to extract substring

Question

Given a hostname in format of aaa0 bbb ccc  I want to extract the first substring before    that is  aaa0 in this case  I use following awk script to do so   echo aaa0 bbb ccc   awk   if  match  0          print substr  0  0  RSTART - 1       While the script running on one machine A produces aaa0  running on machine B produces only aaa  without 0 in the end  Both machine runs Ubuntu Linaro  but A runs newer version of awk gawk with version 3 1 8 while B with older awk  mawk with version 1 2   I am asking in general  how to write a compatible awk script that performs the same functionality

User · Answer

I am asking in general  how to write a compatible awk script that   performs the same functionality       To solve the problem in your quesiton is easy   check others  answer    If you want to write an awk script  which portable to any awk implementations  and versions  gawk nawk mawk     it is really hard  even if with --posix  gawk   for example    some awk works on string in terms of characters  some with bytes some supports  x escape  some not FS interpreter works differently keywords reserved words abbreviation restriction some operator restriction e g     even same awk impl   gawk for example   the version 4 0 and 3 x have difference too  the implementation of certain functions are also different   your problem is one example  see below    well all the points above are just spoken in general  Back to your problem  you problem is only related to fundamental feature of awk  awk   print  x   the line like that will work all awks   There are two reasons why your awk line behaves differently on gawk and mawk    your used substr   function wrongly  this is the main cause  you have substr  0  0  RSTART - 1  the 0 should be 1  no matter which awk do you use  awk array  string idx etc are 1-based  gawk and mawk implemented substr   differently

User · Answer

You just want to set the field separator as   using the -F option and print the first field     echo aaa0 bbb ccc   awk -F      print  1   aaa0   Same thing but using cut     echo aaa0 bbb ccc   cut -d    -f1 aaa0   Or with sed     echo aaa0 bbb ccc   sed  s          aaa0   Even grep     echo aaa0 bbb ccc   grep -o          aaa0

User · Answer

You don t need awk for this     echo aaa0 bbb ccc   cut -d  -f1 cut -d  -f1  lt  lt  lt  aaa0 bbb ccc  echo aaa0 bbb ccc     IFS   read a     echo  a       IFS   read a     echo  a      lt  lt  lt  aaa0 bbb ccc   x aaa0 bbb ccc  echo   x        Heavier options   sed  echo aaa0 bbb ccc   sed  s         sed  s          lt  lt  lt  aaa0 bbb ccc  awk  echo aaa0 bbb ccc   awk -F    print  1   awk -F    print  1    lt  lt  lt  aaa0 bbb ccc

User · Answer

Or just use cut   echo aaa0 bbb ccc   cut -d    -f1

User · Answer

You do not need any external command at all  just use Parameter Expansion in bash   hostname aaa0 bbb ccc echo   hostname

[bash] Use Awk to extract substring

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