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 >&2 -e "\nERROR: $@\n"; exit 1; } run() { "$@"; code=$?; [ $code -ne 0 ] && die "command [$*] 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.

Answer 1

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

!:4 = the fourth parameter of the previous command

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

!^ = the first parameter of the previous command (same as !:1)

!$ = the final parameter of the previous command

!:-3 = all parameters in range 0-3 (inclusive)

!:2-5 = all parameters in range 2-5 (inclusive)

!! = 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 

Answer 2

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.