Echoing the last command run in Bash

Question

I am trying to echo the last command run inside a bash script  I found a way to do it with some history tail head sed which works fine when commands represent a specific line in my script from a parser standpoint  However under some circumstances I don t get the expected output  for instance when the command is inserted inside a case statement   The script      bin bash set -o history date last   echo  history  tail -n2  head -n1    sed  s  0-9        echo  last command is   last    case  1  in    1     date   last   echo  history  tail -n2  head -n1    sed  s  0-9          echo  last command is   last        esac   The output   Tue May 24 12 36 04 CEST 2011 last command is  date  Tue May 24 12 36 04 CEST 2011 last command is  echo  last command is   last       Q  Can someone help me find a way to echo the last run command regardless of how where this command is called within the bash script   My answer  Despite the much appreciated contributions from my fellow SO ers  I opted for writing a run function - which runs all its parameters as a single command and display the command and its error code when it fails - with the following benefits  -I only need to prepend the commands I want to check with run which keeps them on one line and doesn t affect the conciseness of my script -Whenever the script fails on one of these commands  the last output line of my script is a message that clearly displays which command fails along with its exit code  which makes debugging easier  Example script      bin bash die     echo  gt  amp 2 -e   nERROR     n   exit 1    run           code        code -ne 0    amp  amp  die  command      failed with error code  code      case  1  in    1     run ls  opt   run ls  wrong-dir      esac   The output       test sh apacheds  google  iptables ls  cannot access  wrong-dir  No such file or directory  ERROR  command  ls  wrong-dir  failed with error code 2   I tested various commands with multiple arguments  bash variables as arguments  quoted arguments    and the run function didn t break them  The only issue I found so far is to run an echo which breaks but I do not plan to check my echos anyway

User · Answer

Bash has built in features to access the last command executed. But that's the last whole command (e.g. the whole case command), not individual simple commands like you originally requested.

!:0 = the name of command executed.

!:1 = the first parameter of the previous command

!:* = all of the parameters of the previous command

!:-1 = the final parameter of the previous command

!! = the previous command line

etc.

So, the simplest answer to the question is, in fact:

echo !!

...alternatively:

echo "Last command run was ["!:0"] with arguments ["!:*"]"

Try it yourself!

echo this is a test
echo !!

In a script, history expansion is turned off by default, you need to enable it with

set -o history -o histexpand

User · Answer

history   tail -2   head -1   cut -c8-999  tail -2 returns the last two command lines from history  head -1 returns just first line cut -c8-999 returns just command line  removing PID and spaces

User · Answer

I was able to achieve this by using set -x in the main script  which makes the script print out every command that is executed  and writing a wrapper script which just shows the last line of output generated by set -x   This is the main script      bin bash set -x echo some command here echo last command   And this is the wrapper script      bin sh   test sh 2 gt  amp 1   grep         tail -n 1   sed -e  s           Running the wrapper script produces this as output   echo last command

User · Answer

After reading the answer from Gilles  I decided to see if the  BASH COMMAND var was also available  and the desired value  in an EXIT trap - and it is   So  the following bash script works as expected      bin bash  exit trap        local lc   BASH COMMAND  rc      echo  Command   lc  exited with code   rc      trap exit trap EXIT set -e  echo  foo  false 12345 echo  bar    The output is  foo Command  false 12345  exited with code  1    bar is never printed because set -e causes bash to exit the script when a command fails and the false command always fails  by definition   The 12345 passed to false is just there to show that the arguments to the failed command are captured as well  the false command ignores any arguments passed to it

User · Answer

There is a racecondition between the last command      and last error       variables  If you try to store one of them in an own variable  both encountered new values already because of the set command  Actually  last command hasn t got any value at all in this case   Here is what i did to store  nearly  both informations in own variables  so my bash script can determine if there was any error AND setting the title with the last run command        This construct is needed  because of a racecondition when trying to obtain      both of last command and error  With this the information of last error is      implied by the corresponding case while command is retrieved      if                0  amp  amp                    then       Last command MUST be retrieved first        LASTCOMMAND                RETURNSTATUS          elif              0  amp  amp                    then       LASTCOMMAND  unknown          RETURNSTATUS          elif              0  amp  amp                    then       Last command MUST be retrieved first        LASTCOMMAND                RETURNSTATUS               Fixme       not changing state until command executed     elif              0  amp  amp                    then       LASTCOMMAND  unknown          RETURNSTATUS               Fixme       not changing state until command executed     fi   This script will retain the information  if an error occured and will obtain the last run command  Because of the racecondition i can not store the actual value  Besides  most commands actually don t even care for error noumbers  they just return something different from  0   You ll notice that  if you use the errono extention of bash   It should be possible with something like a  intern  script for bash  like in bash extention  but i m not familiar with something like that and it wouldn t be compatible as well   CORRECTION  I didn t think  that it was possible to retrieve both variables at the same time  Although i like the style of the code  i assumed it would be interpreted as two commands  This was wrong  so my answer devides down to        Because of a racecondition  both MUST be retrieved at the same time     declare RETURNSTATUS        LASTCOMMAND              if       RETURNSTATUS      0      then       declare RETURNSYMBOL          else       declare RETURNSYMBOL          fi   Although my post might not get any positive rating  i solved my problem myself  finally  And this seems appropriate regarding the intial post

User · Answer

The command history is an interactive feature  Only complete commands are entered in the history  For example  the case construct is entered as a whole  when the shell has finished parsing it  Neither looking up the history with the history built-in  nor printing it through shell expansion    p   does what you seem to want  which is to print invocations of simple commands   The DEBUG trap lets you execute a command right before any simple command execution  A string version of the command to execute  with words separated by spaces  is available in the BASH COMMAND variable   trap  previous command  this command  this command  BASH COMMAND  DEBUG     echo  last command is  previous command    Note that previous command will change every time you run a command  so save it to a variable in order to use it  If you want to know the previous command s return status as well  save both in a single command   cmd  previous command ret    if    ret -ne 0    then echo   cmd failed with error code  ret   fi   Furthermore  if you only want to abort on a failed commands  use set -e to make your script exit on the first failed command  You can display the last command from the EXIT trap   set -e trap  echo  exit    due to  previous command   EXIT   Note that if you re trying to trace your script to see what it s doing  forget all this and use set -x

[bash] Echoing the last command run in Bash?

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