How to use shell commands in Makefile

Question

I m trying to use the result of ls in other commands  e g  echo  rsync    all       lt Building  creating some  tgz files - removed for clarity gt      FILES     shell ls      echo   FILES    But I get   make FILES   Makefile file1 tgz file2 tgz file3 tgz make  FILES  No such file or directory make       all  Error 1   I ve tried using echo   FILES  echo   FILES  and echo   FILES   with no luck

User · Answer

Also  in addition to torek s answer  one thing that stands out is that you re using a lazily-evaluated macro assignment   If you re on GNU Make  use the    assignment instead of    This assignment causes the right hand side to be expanded immediately  and stored in the left hand variable   FILES      shell         expand now  FILES is now the result of   shell       FILES     shell          expand later  FILES holds the syntax   shell        If you use the   assignment  it means that every single occurrence of   FILES  will be expanding the   shell      syntax and thus invoking the shell command  This will make your make job run slower  or even have some surprising consequences

User · Answer

With   FILES     shell ls    indented underneath all like that  it s a build command   So this expands   shell ls   then tries to run the command FILES       If FILES is supposed to be a make variable  these variables need to be assigned outside the recipe portion  e g    FILES     shell ls  all          echo   FILES    Of course  that means that FILES will be set to  output from ls  before running any of the commands that create the  tgz files    Though as Kaz notes the variable is re-expanded each time  so eventually it will include the  tgz files  some make variants have FILES        to avoid this  for efficiency and or correctness 1   If FILES is supposed to be a shell variable  you can set it but you need to do it in shell-ese  with no spaces  and quoted   all          FILES    shell ls     However  each line is run by a separate shell  so this variable will not survive to the next line  so you must then use it immediately           FILES    shell ls    echo   FILES   This is all a bit silly since the shell will expand    and other shell glob expressions  for you in the first place  so you can just           echo     as your shell command   Finally  as a general rule  not really applicable to this example   as esperanto notes in comments  using the output from ls is not completely reliable  some details depend on file names and sometimes even the version of ls  some versions of ls attempt to sanitize output in some cases    Thus  as l0b0 and idelic note  if you re using GNU make you can use   wildcard  and   subst      to accomplish everything inside make itself  avoiding any  weird characters in file name  issues     In sh scripts  including the recipe portion of makefiles  another method is to use find     -print0   xargs -0 to avoid tripping over blanks  newlines  control characters  and so on      1The GNU Make documentation notes further that POSIX make added     assignment in 2012   I have not found a quick reference link to a POSIX document for this  nor do I know off-hand which make variants support     assignment  although GNU make does today  with the same meaning as     i e   do the assignment right now with expansion   Note that VAR      shell command args     can also be spelled VAR    command args    in several make variants  including all modern GNU and BSD variants as far as I know   These other variants do not have   shell  so using VAR    command args    is superior in both being shorter and working in more variants

[bash] How to use shell commands in Makefile

Examples related to bash

Examples related to makefile

Examples related to echo