Read line by line in bash script

Question

I want to do the following  read line by line of a file and use the value per line as params  FILE  cat test  echo   FILE      while read CMD  do echo  CMD done   but when I do the echo  CMD  it just returns cat  S

User · Answer

FILE test  while read CMD  do     echo   CMD  done  lt    FILE    A redirection with  lt    FILE  has a few advantages over cat   FILE    while      It avoids a useless use of cat  saving an unnecessary child process  It also avoids a common pitfall where the loop runs in a subshell  In bash  commands in a   pipeline run in subshells  which means variable assignments are lost after the loop ends  Redirection with  lt  doesn t have that problem  so you could use  CMD after the loop or modify other variables inside the loop  It also  again  avoids unnecessary child processes   There are some additional improvements that could be made    Add IFS  so that read won t trim leading and trailing whitespace from each line  Add -r to read to prevent from backslashes from being interpreted as escape sequences  Lower case CMD and FILE  The bash convention is only environmental and internal shell variables are uppercase  Use printf in place of echo which is safer if  cmd is a string like -n  which echo would interpret as a flag    file test  while IFS  read -r cmd  do     printf   s n    cmd  done  lt    file

User · Answer

If you want to use each of the lines of the file as command-line params for your application you can use the xargs command   xargs -a  lt params file gt   lt command gt    A params file with   a b c d   and the file tr py   import sys print sys argv   The execution of   xargs -a params   tr py   gives the result       tr py    a    b    c    d

User · Answer

xargs is the most flexible solution for splitting output into command arguments   It is also very human readable and easy to use due to its simple parameterisation   Format is xargs -n  NUMLINES mycommand   For example  to echo each individual line in a file  tmp tmp txt you d do   cat  tmp tmp txt   xargs -n 1 echo   Or to diff each successive pair of files listed as lines in a file of the above name you d do   cat  tmp tmp txt   xargs -n 2 diff   The -n 2 instructs xargs to consume and pass as separate arguments two lines of what you ve piped into it at a time   You can tailor xargs to split on delimiters besides carriage return newline   Use man xargs and google to find out more about the power of this versatile utility

User · Answer

What you have is piping the text  cat test  into the loop   You just want   cat test     while read CMD  do     echo  CMD done

User · Answer

Do you mean to do   cat test     while read CMD  do echo  CMD done

User · Answer

The correct version of your script is as follows   FILE  cat test   FILE     while read CMD  do echo  CMD done   However this kind of indirection --putting your command in a variable named FILE-- is unnecessary  Use one of the solutions already provided  I just wanted to point out your mistake

User · Answer

while read CMD  do     echo  CMD done   lt  lt  EOF data line 1 data line 2    EOF

[linux] Read line by line in bash script

Examples related to linux

Examples related to bash