Validating parameters to a Bash script

Question

I came up with a basic one to help automate the process of removing a number of folders as they become unneeded      bin bash rm -rf   myfolder1  1 anotherfolder rm -rf   myfolder2  1 yetanotherfolder rm -rf   myfolder3  1 thisisafolder   This is evoked like so     myscript sh  lt  id-number  gt    The problem is that if you forget to type in the id-number  as I did just then   then it could potentially delete a lot of things that you really don t want deleted   Is there a way you can add any form of validation to the command line parameters  In my case  it d be good to check that a  there is one parameter  b  it s numerical  and c  that folder exists  before continuing with the script

User · Answer

You can validate point a and b compactly by doing something like the following:

#!/bin/sh
MYVAL=$(echo ${1} | awk '/^[0-9]+$/')
MYVAL=${MYVAL:?"Usage - testparms <number>"}
echo ${MYVAL}

Which gives us ...

$ ./testparams.sh 
Usage - testparms <number>

$ ./testparams.sh 1234
1234

$ ./testparams.sh abcd
Usage - testparms <number>

This method should work fine in sh.

User · Answer

one liner Bash argument validation  with and without directory validation  Here are some methods that have worked for me  You can use them in either the global script namespace  if in the global namespace  you can t reference the function builtin variables   quick and dirty one liner      1   You forgot to supply a directory name     output     my script  line 279  1  You forgot to supply a directory name   Fancier - supply function name and usage    1  ERROR Function    FUNCNAME 0     Usage      FUNCNAME 0   directory name     output     my script  line 288  1   ERROR Function  deleteFolders   Usage   deleteFolders directory name   Add complex validation logic without cluttering your current function  Add the following line within the function or script that receives the argument       1  forgot to supply a directory name    amp  amp  validate  1    die  Please supply a valid directory    You can then create a validation function that does something like  validate           validate input and   amp  return 1 if failed  0 if succeed     if      -d   1      then         return 1     fi     and a die function that aborts the script on failure   die     echo      1 gt  amp 2   exit 1      For additional arguments  just add an additional line  replicating the format       1   You forgot to supply the first argument       2   You forgot to supply the second argument

User · Answer

Not as bulletproof as the above answer  however still effective      bin bash if     1         then   echo  Usage   0  lt id number to be cleaned up gt     exit fi    rm commands go here

User · Answer

Use  -z  to test for empty strings and  -d to check for directories   if    -z          then     echo  gt  amp 2  You must supply an argument       exit 1 elif      -d          then     echo  gt  amp 2     is not a valid directory       exit 1 fi

User · Answer

Old post but I figured i could contribute anyway  A script is arguably not necessary and with some tolerance to wild cards could be carried out from the command line   wild anywhere matching  Lets remove any occurrence of sub  quot folder quot     rm -rf     folder      Shell iterated  Lets remove the specific pre and post folders with one line    rm -rf   foo 1 2 3  folder  ab cd ef     Shell iterated   var  BASH tested      var bar rm -rf   foo 1 2 3    var   ab cd ef

User · Answer

I would use bash s      if               1  amp  amp   1      0-9     amp  amp  -d  1      then      echo  Please pass a number that corresponds to a directory      exit 1 fi   I found this faq to be a good source of information

User · Answer

bin sh die          echo  gt  amp 2          exit 1           -eq 1      die  1 argument required     provided  echo  1   grep -E -q    0-9        die  Numeric argument required   1 provided   while read dir  do       -d   dir       die  Directory  dir does not exist      rm -rf   dir  done  lt  lt EOF   myfolder1  1 anotherfolder    myfolder2  1 yetanotherfolder    myfolder3  1 thisisafolder EOF   edit  I missed the part about checking if the directories exist at first  so I added that in  completing the script  Also  have addressed issues raised in comments  fixed the regular expression  switched from    to eq   This should be a portable  POSIX compliant script as far as I can tell  it doesn t use any bashisms  which is actually important because  bin sh on Ubuntu is actually dash these days  not bash

User · Answer

Use set -u which will cause any unset argument reference to immediately fail the script  Please  see the article  Writing Robust Bash Shell Scripts - David Pashley com

User · Answer

The sh solution by Brian Campbell  while noble and well executed  has a few problems  so I thought I d provide my own bash solution   The problems with the sh one    The tilde in   foo doesn t expand to your homedirectory inside heredocs   And neither when it s read by the read statement or quoted in the rm statement   Which means you ll get No such file or directory errors  Forking off grep and such for basic operations is daft   Especially when you re using a crappy shell to avoid the  heavy  weight of bash  I also noticed a few quoting issues  for instance around a parameter expansion in his echo  While rare  the solution cannot cope with filenames that contain newlines   Almost no solution in sh can cope with them - which is why I almost always prefer bash  it s far more bulletproof  amp  harder to exploit when used well     While  yes  using  bin sh for your hashbang means you must avoid bashisms at all costs  you can use all the bashisms you like  even on Ubuntu or whatnot when you re honest and put    bin bash at the top   So  here s a bash solution that s smaller  cleaner  more transparent  probably  faster   and more bulletproof      -d  1  amp  amp   1       0-9           echo  Invalid input    gt  amp 2  exit 1    rm -rf   foo   1  bar        Notice the quotes around  1 in the rm statement  The -d check will also fail if  1 is empty  so that s two checks in one  I avoided regular expressions for a reason   If you must use    in bash  you should be putting the regular expression in a variable   In any case  globs like mine are always preferable and supported in far more bash versions

User · Answer

The man page for test  man test  provides all available operators you can use as boolean operators in bash   Use those flags in the beginning of your script  or functions  for input validation just like you would in any other programming language  For example   if   -z  1     then   echo  First parameter needed    amp  amp  exit 1  fi  if   -z  2     then   echo  Second parameter needed    amp  amp  exit 2  fi

[validation] Validating parameters to a Bash script

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