Capturing multiple line output into a Bash variable

Question

I ve got a script  myscript  that outputs the following   abc def ghi   in another script  I call   declare RESULT     myscript    and  RESULT gets the value  abc def ghi   Is there a way to store the result either with the newlines  or with   n  character so I can output it with  echo -e

User · Answer

How about this  it will read each line to a variable and that can be used subsequently    say myscript output is redirected to a file called  myscript output  awk   while    getline var  lt   myscript output    gt 0  print var   close   myscript output

User · Answer

In case that you re interested in specific lines  use a result-array   declare RESULT      myscript             array echo  First line    RESULT 0    echo  Second line    RESULT 1    echo  N-th line    RESULT N

User · Answer

Parsing multiple output Introduction So your myscript output 3 lines  could look like  myscript     echo   abc ndef nghi      or myscript     local i  for i in abc def ghi  do echo  i  done     Ok this is a function  not a script  no need of path      but output is same myscript abc def ghi  Considering result code To check for result code  test function will become  myscript     local i for i in abc def ghi  do echo  i done return    RANDOM 128      1  Storing multiple output in one single variable  showing newlines Your operation is correct  RESULT   myscript   About result code  you could add  RCODE     even in same line  RESULT   myscript  RCODE     Then echo  RESULT  abc def ghi  echo  quot  RESULT quot  abc def ghi  echo   RESULT Q    abc ndef nghi   printf  quot  q n quot   quot  RESULT quot    abc ndef nghi   but for showing variable definition  use declare -p  declare -p RESULT declare -- RESULT  quot abc def ghi quot   2  Parsing multiple output in array  using mapfile Storing answer into myvar variable  mapfile -t myvar  lt   lt  myscript  echo   myvar 2   ghi  Showing  myvar  declare -p myvar declare -a myvar   0   quot abc quot   1   quot def quot   2   quot ghi quot    Considering result code In case you have to check for result code  you could  RESULT   myscript  RCODE    mapfile -t myvar  lt  lt  lt  quot  RESULT quot   3  Parsing multiple output by consecutives read in command group   read firstline  read secondline  read thirdline    lt   lt  myscript  echo  secondline def  Showing variables  declare -p firstline secondline thirdline declare -- firstline  quot abc quot  declare -- secondline  quot def quot  declare -- thirdline  quot ghi quot   I often use    read foo read foo total use free foo     lt   lt  df -k     Then declare -p use free total declare -- use  quot 843476 quot  declare -- free  quot 582128 quot  declare -- total  quot 1515376 quot   Considering result code Same prepended step  RESULT   myscript  RCODE      read firstline  read secondline  read thirdline    lt  lt  lt  quot  RESULT quot   declare -p firstline secondline thirdline RCODE declare -- firstline  quot abc quot  declare -- secondline  quot def quot  declare -- thirdline  quot ghi quot  declare -- RCODE  quot 50 quot

User · Answer

After trying most of the solutions here  the easiest thing I found was the obvious - using a temp file  I m not sure what you want to do with your multiple line output  but you can then deal with it line by line using read  About the only thing you can t really do is easily stick it all in the same variable  but for most practical purposes this is way easier to deal with     myscript sh  gt   tmp foo while read line   do      echo  whatever you want to do with  line  done  lt   tmp foo   Quick hack to make it do the requested action   result      myscript sh  gt   tmp foo while read line   do   result   result line n  done  lt   tmp foo echo -e  result   Note this adds an extra line  If you work on it you can code around it  I m just too lazy     EDIT  While this case works perfectly well  people reading this should be aware that you can easily squash your stdin inside the while loop  thus giving you a script that will run one line  clear stdin  and exit  Like ssh will do that I think  I just saw it recently  other code examples here  https   unix stackexchange com questions 24260 reading-lines-from-a-file-with-bash-for-vs-while  One more time  This time with a different filehandle  stdin  stdout  stderr are 0-2  so we can use  amp 3 or higher in bash    result      test gt  tmp foo while read line   lt  amp 3  do     result   result line n  done 3 lt  tmp foo echo -e  result   you can also use mktemp  but this is just a quick code example  Usage for mktemp looks like   filenamevar  mktemp  tmp tempXXXXXX    test  gt   filenamevar   Then use  filenamevar like you would the actual name of a file  Probably doesn t need to be explained here but someone complained in the comments

User · Answer

Another pitfall with this is that command substitution             strips trailing newlines  Probably not always important  but if you really want to preserve exactly what was output  you ll have to use another line and some quoting   RESULTX      myscript  echo x   RESULT    RESULTX x     This is especially important if you want to handle all possible filenames  to avoid undefined behavior like operating on the wrong file

User · Answer

In addition to the answer given by  l0b0 I just had the situation where I needed to both keep any trailing newlines output by the script and check the script s return code  And the problem with l0b0 s answer is that the  echo x  was resetting    back to zero    so I managed to come up with this very cunning solution   RESULTX      myscript  echo x     RETURNCODE   RESULTX   x  RESULT    RESULTX x

User · Answer

Actually  RESULT contains what you want     to demonstrate   echo   RESULT    What you show is what you get from   echo  RESULT     As noted in the comments  the difference is that  1  the double-quoted version of the variable  echo   RESULT   preserves internal spacing of the value exactly as it is represented in the variable     newlines  tabs  multiple blanks and all     whereas  2  the unquoted version  echo  RESULT  replaces each sequence of one or more blanks  tabs and newlines with a single space  Thus  1  preserves the shape of the input variable  whereas  2  creates a potentially very long single line of output with  words  separated by single spaces  where a  word  is a sequence of non-whitespace characters  there needn t be any alphanumerics in any of the words

[bash] Capturing multiple line output into a Bash variable

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