Calling an executable program using awk

Question

I have a program in C that I want to call by using awk in shell scripting  How can I do something like this

User · Answer

I was able to have this done via below method

cat ../logs/em2.log.1 |grep -i 192.168.21.15 |awk '{system(`date`); print $1}'

awk has a function called system it enables you to execute any linux bash command within the output of awk.

User · Answer

It really depends    One of the handy linux core utils  info coreutils  is xargs  If you are using awk you probably have a more involved  use-case in mind - your question is not very detailled   printf  1 2 n3 4    awk    print  2      xargs touch   Will execute touch 2 4  Here touch could be replaced by your program  More info at info xargs and man xargs  really  read these   I believe you would like to replace touch with your program   Breakdown of beforementioned script   printf  1 2 n3 4    Output  1 2 3 4    The pipe     makes the output of the left command the input of   the right command  simplified  printf  1 2 n3 4    awk    print  2      Output  of the awk command   2 4    xargs will execute a command with arguments  The arguments   are made up taking the input to xargs  in this case the output   of the awk command  which is  2 4   printf  1 2 n3 4    awk    print  2      xargs touch   No output  but executes   touch 2 4  which will create  or update   timestamp if the files already exist  files with the name  2  and  4    Update In the original answer  I used echo instead of printf  However  printf is the better and more portable alternative as was pointed out by a comment  where great links with discussions can be found

User · Answer

Something as simple as this will work  awk  BEGIN system  echo hello       and  awk  BEGIN   system  date    close  date

User · Answer

usr bin awk -f  BEGIN       command    ls -lh       command  getline     Runs  ls -lh  in an awk script

User · Answer

From the AWK man page    system cmd                executes cmd and returns its exit status   The GNU AWK manual also has a section that  in part  describes the system function and provides an example   system  date   mail -s  awk run done  root

User · Answer

A much more robust way would be to use the getline   function of GNU awk to use a variable from a pipe  In form cmd   getline result  cmd is run  then its output is piped to getline  It returns 1 if got output  0 if EOF  -1 on failure  First construct the command to run in a variable in the BEGIN clause if the command is not dependant on the contents of the file  e g  a simple date or an ls  A simple example of the above would be awk  BEGIN       cmd    quot ls -lrth quot      while     cmd   getline result    gt  0             print result           close cmd       When the command to run is part of the columnar content of a file  you generate the cmd string in the main      as below  E g  consider a file whose  2 contains the name of the file and you want it to be replaced with the md5sum hash content of the file  You can do awk    cmd    quot md5sum  quot  2        while     cmd   getline md5result    gt  0                  2   md5result                 close cmd     1   Another frequent usage involving external commands in awk is during date processing when your awk does not support time functions out of the box with mktime    strftime   functions  Consider a case when you have Unix EPOCH timestamp stored in a column and you want to convert that to a human readable date format  Assuming GNU date is available awk    cmd    quot date -d   quot   1  quot     quot  d- m- Y  H  M  S  quot  quot          while     cmd   getline fmtDate   gt  0                  1   fmtDate                 close cmd    1    for an input string as 1572608319 foo bar zoo  the above command produces an output as 01-11-2019 07 38 39 foo bar zoo  The command can be tailored to modify the date fields on any of the columns in a given line  Note that -d is a GNU specific extension  the  BSD variants support -f   though not exactly similar to -d   More information about getline can be referred to from this AllAboutGetline article at awk freeshell org page

User · Answer

I use the power of awk to delete some of my stopped docker containers  Observe carefully how i construct the cmd string first before passing it to system    docker ps -a   awk   3     bin clish    cmd  docker rm   1 system cmd     Here  I use the 3rd column having the pattern   bin clish  and then I extract the container ID in the first column to construct my cmd string and passed that to system

User · Answer

There are several ways    awk has a system   function that will run a shell command   system  cmd   You can print to a pipe   print  blah     cmd  You can have awk construct commands  and pipe all the output to the shell   awk  some script    sh

[shell] Calling an executable program using awk

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