How to determine the current shell I m working on

Question

How can I determine the current shell I am working on    Would the output of the ps command alone be sufficient   How can this be done in different flavors of Unix

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echo      Gives the Parent Process ID  ps -ef   grep      awk   print  8     Use the PID to see what the process is    From How do you know what your current shell is

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This one works well on Red Hat Linux  RHEL   macOS  BSD and some AIXes   ps -T      awk  NR  2 print  NF      alternatively  the following one should also work if pstree is available   pstree   egrep      awk  NR  2 print  NF

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ps is the most reliable method  The SHELL environment variable is not guaranteed to be set and even if it is  it can be easily spoofed

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You can try   ps   grep  echo       awk    print  4      Or   echo  SHELL

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There are three approaches to finding the name of the current shell s executable   Please note that all three approaches can be fooled if the executable of the shell is  bin sh  but it s really a renamed bash  for example  which frequently happens    Thus your second question of whether ps output will do is answered with  not always     echo  0 - will print the program name    which in the case of the shell is the actual shell  ps  -ef   grep      grep -v grep - this will look for the current process ID in the list of running processes  Since the current process is the shell  it will be included   This is not 100  reliable  as you might have other processes whose ps listing includes the same number as shell s process ID  especially if that ID is a small number  for example  if the shell s PID is  5   you may find processes called  java5  or  perl5  in the same grep output    This is the second problem with the  ps  approach  on top of not being able to rely on the shell name  echo  SHELL - The path to the current shell is stored as the SHELL variable for any shell  The caveat for this one is that if you launch a shell explicitly as a subprocess  for example  it s not your login shell   you will get your login shell s value instead  If that s a possibility  use the ps or  0 approach     If  however  the executable doesn t match your actual shell  e g   bin sh is actually bash or ksh   you need heuristics  Here are some environmental variables specific to various shells     version is set on tcsh  BASH is set on bash  shell  lowercase  is set to actual shell name in csh or tcsh  ZSH NAME is set on zsh ksh has  PS3 and  PS4 set  whereas the normal Bourne shell  sh  only has  PS1 and  PS2 set  This generally seems like the hardest to distinguish - the only difference in the entire set of environment variables between sh and ksh we have installed on Solaris boxen is  ERRNO   FCEDIT   LINENO   PPID   PS3   PS4   RANDOM   SECONDS  and  TMOUT

User · Answer

Grepping PID from the output of  ps  is not needed  because you can read the respective command line for any PID from the  proc directory structure   echo   cat  proc    cmdline    However  that might not be any better than just simply   echo  0   About running an actually different shell than the name indicates  one idea is to request the version from the shell using the name you got previously    lt some shell gt  --version   sh seems to fail with exit code 2 while others give something useful  but I am not able to verify all since I don t have them      sh --version sh  0  Illegal option -- echo    2

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My solution   ps -o command   grep -v -e    lt ps  gt   -e grep -e tail   tail -1   This should be portable across different platforms and shells  It uses ps like other solutions  but it doesn t rely on sed or awk and filters out junk from piping and ps itself so that the shell should always be the last entry  This way we don t need to rely on non-portable PID variables or picking out the right lines and columns   I ve tested on Debian and macOS with Bash  Z shell  zsh   and fish  which doesn t work with most of these solutions without changing the expression specifically for fish  because it uses a different PID variable

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If you just want to ensure the user is invoking a script with Bash   if     -n   BASH     then echo Please run this script  0 with bash  exit 1  fi

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Try  ps -p    -oargs    or  ps -p    -ocomm

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My variant on printing the parent process   ps -p      awk   1    PP  print  4   PP      Don t run unnecessary applications when AWK can do it for you

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I have a simple trick to find the current shell  Just type a random string  which is not a command   It will fail and return a  not found  error  but at start of the line it will say which shell it is   ksh  aaaaa  not found  No such file or directory  bash  aaaaa  command not found

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On Mac OS X  and FreeBSD    ps -p    -axco command   sed -n   p

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Provided that your  bin sh supports the POSIX standard and your system has the lsof command installed - a possible alternative to lsof could in this case be pid2path - you can also use  or adapt  the following script that prints full paths      bin sh   cat  usr local bin cursh set -eu pid       set -- sh bash zsh ksh ash dash csh tcsh pdksh mksh fish psh rc scsh bournesh wish Wish login  unset echo env sed ps lsof awk getconf    getconf  POSIX VERSION    reliable test for availability of POSIX system  PATH   PATH  usr bin  bin  usr sbin  sbin getconf PATH        -ne 0    amp  amp    echo   getconf PATH  failed   exit 1    export PATH  cmd  lsof  env -i PATH    PATH   type   cmd  1 gt  dev null 2 gt  amp 1      echo   cmd not found   exit 1     awkstr   echo        sed  s         1          1 g  s     g    sed  s       s          ppid   env -i PATH    PATH   ps -p  pid -o ppid         ppid  X     X    amp  amp    echo  no ppid found   exit 1     lsofstr   lsof -p  ppid            printf   s n   lsof failed   try  sudo lsof -p   ps -p      -o ppid      exit 1     printf   s n     lsofstr         LC ALL C awk -v var    awkstr     NF   var  print  NF

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And i came up with this  sed  s   SHELL     s    upper          proc    environ

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Do the following to know whether your shell is using Dash Bash   ls    la  bin sh    if the result is  bin sh - gt   bin bash     Then your shell is using Bash  if the result is  bin sh - gt  bin dash     Then your shell is using Dash    If you want to change from Bash to Dash or vice-versa  use the below code   ln -s  bin bash  bin sh  change shell to Bash   Note  If the above command results in a error saying   bin sh already exists  remove the  bin sh and try again

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The following will always give the actual shell used - it gets the name of the actual executable and not the shell name  i e  ksh93 instead of ksh  etc    For  bin sh  it will show the actual shell used  i e  dash   ls -l  proc    exe   sed  s          I know that there are many who say the ls output should never be processed  but what is the probability you ll have a shell you are using that is named with special characters or placed in a directory named with special characters  If this is still the case  there are plenty of other examples of doing it differently   As pointed out by Toby Speight  this would be a more proper and cleaner way of achieving the same   basename   readlink  proc    exe

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I have tried many different approaches and the best one for me is   ps -p      It also works under Cygwin and cannot produce false positives as PID grepping  With some cleaning  it outputs just an executable name  under Cygwin with path    ps -p      tail -1   awk   print  NF     You can create a function so you don t have to memorize it     Print currently active shell shell        ps -p      tail -1   awk   print  NF          and then just execute shell   It was tested under Debian and Cygwin

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There are many ways to find out the shell and its corresponding version  Here are few which worked for me   Straightforward      echo  0  Gives you the program name  In my case the output was -bash       SHELL  This takes you into the shell and in the prompt you get the shell name and version  In my case bash3 2       echo  SHELL  This will give you executable path  In my case  bin bash       SHELL --version  This will give complete info about the shell software with license type    Hackish approach              Type a set of random characters and in the output you will get the shell name  In my case -bash  chapter2-a-sample-isomorphic-app  command not found

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Kindly use the below command   ps -p      tail -1   awk   print  4

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This is not a very clean solution  but it does what you want     MUST BE SOURCED   getshell         local shell   ps -p      tail -1   awk   print  4          shells array         It is important that the shells are listed in descending order of their name length          pdksh         bash dash mksh         zsh ksh         sh            local suited false     for i in   shells array      do         if     -z  printf  shell   grep  i     amp  amp     suited  then             shell  i             suited true         fi     done      echo  shell   getshell   Now you can use   getshell  --version   This works  though  only on KornShell-like shells  ksh

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If you just want to check that you are running  a particular version of  Bash  the best way to do so is to use the  BASH VERSINFO array variable  As a  read-only  array variable it cannot be set in the environment  so you can be sure it is coming  if at all  from the current shell   However  since Bash has a different behavior when invoked as sh  you do also need to check the  BASH environment variable ends with  bash   In a script I wrote that uses function names with -  not underscore   and depends on associative arrays  added in Bash 4   I have the following sanity check  with helpful user error message    case  eval  echo  BASH   BASH VERSINFO 0    2 gt  dev null  in       bash  456789             Claims bash version 4   check for func-names and associative arrays         if   eval  declare -A  ARRAY  amp  amp  func-name           2 gt  dev null  then             echo  gt  amp 2  bash  BASH VERSION is not supported  not really bash                exit 1         fi                  bash  123           echo  gt  amp 2  bash  BASH VERSION is not supported  version 4  required           exit 1                           echo  gt  amp 2  This script requires BASH  version 4   - not regular sh          echo  gt  amp 2  Re-run as   bash  CMD   for proper operation          exit 1            esac   You could omit the somewhat paranoid functional check for features in the first case  and just assume that future Bash versions would be compatible

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SHELL need not always show the current shell  It only reflects the default shell to be invoked   To test the above  say bash is the default shell  try echo  SHELL  and then in the same terminal  get into some other shell  KornShell  ksh  for example  and try  SHELL  You will see the result as bash in both cases   To get the name of the current shell  Use cat  proc    cmdline  And the path to the shell executable by readlink  proc    exe

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ps -p     should work anywhere that the solutions involving ps -ef and grep do  on any Unix variant which supports POSIX options for ps  and will not suffer from the false positives introduced by grepping for a sequence of digits which may appear elsewhere

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None of the answers worked with fish shell  it doesn t have the variables    or  0    This works for me  tested on sh  bash  fish  ksh  csh  true  tcsh  and zsh  openSUSE 13 2    ps   tail -n 4   sed -E  2  d s          1     This command outputs a string like bash  Here I m only using ps  tail  and sed  without GNU extesions  try to add --posix to check it   They are all standard POSIX commands  I m sure tail can be removed  but my sed fu is not strong enough to do this   It seems to me  that this solution is not very portable as it doesn t work on OS X

[bash] How to determine the current shell I'm working on

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