How to echo shell commands as they are executed

Question

In a shell script, how do I echo all shell commands called and expand any variable names?

For example, given the following line:

ls $DIRNAME

I would like the script to run the command and display the following

ls /full/path/to/some/dir

The purpose is to save a log of all shell commands called and their arguments. Is there perhaps a better way of generating such a log?

Answer 1

set -x or set -o xtrace expands variables and prints a little + sign before the line.

set -v or set -o verbose does not expand the variables before printing.

Use set +x and set +v to turn off the above settings.

On the first line of the script, one can put #!/bin/sh -x (or -v) to have the same effect as set -x (or -v) later in the script.

The above also works with /bin/sh.

See the bash-hackers' wiki on set attributes, and on debugging.

$ cat shl
#!/bin/bash                                                                     

DIR=/tmp/so
ls $DIR

$ bash -x shl 
+ DIR=/tmp/so
+ ls /tmp/so
$

Answer 2

set -x will give you what you want.

Here is an example shell script to demonstrate:

#!/bin/bash
set -x #echo on

ls $PWD

This expands all variables and prints the full commands before output of the command.

output:

+ ls /home/user/
file1.txt file2.txt

Answer 3

You can also toggle this for select lines in your script by wrapping them in set -x and set +x e.g.

#!/bin/bash
...
if [[ ! -e $OUT_FILE ]];
then
   echo "grabbing $URL"
   set -x
   curl --fail --noproxy $SERV -s -S $URL -o $OUT_FILE
   set +x
fi

Answer 4

I use a function to echo then run the command

#!/bin/bash
#function to display commands
exe() { echo "\$ $@" ; "$@" ; }

exe echo hello world

Which outputs

$ echo hello world
hello world

Edit:

For more complicated commands pipes etc you can use eval:

#!/bin/bash
#function to display commands
exe() { echo "\$ ${@/eval/}" ; "$@" ; }

exe eval "echo 'Hello World' | cut -d ' ' -f1"

Which outputs

$  echo 'Hello World' | cut -d ' ' -f1
Hello

Answer 5

shuckc's answer for echoing select lines has a few downsides: you end up with the following set +x command being echoed as well, and you lose the ability to test the exit code with $? since it gets overwritten by the set +x.

Another option is to run the command in a subshell:

echo "getting URL..."
( set -x ; curl -s --fail $URL -o $OUTFILE )

if [ $? -eq 0 ] ; then
    echo "curl failed"
    exit 1
fi

which will give you output like:

getting URL...
+ curl -s --fail http://example.com/missing -o /tmp/example
curl failed

This does incur the overhead of creating a new subshell for the command, though.

Answer 6

Another option is to put "-x" at the top of your script instead of on the command line:

$ cat ./server
#!/bin/bash -x
ssh user@server

$ ./server
+ ssh user@server
user@server's password: ^C
$

(Insufficient rep to comment on chosen answer.)

Answer 7

According to TLDP's Bash Guide for Beginners: Chapter 2. Writing and debugging scripts

2.3.1. Debugging on the entire script

$ bash -x script1.sh

...

There is now a full-fledged debugger for Bash, available at SourceForge. These debugging features are available in most modern versions of Bash, starting from 3.x.

2.3.2. Debugging on part(s) of the script

set -x            # activate debugging from here
w
set +x            # stop debugging from here

...

Table 2-1. Overview of set debugging options

Short  | Long notation | Result  
-------+---------------+--------------------------------------------------------------
set -f | set -o noglob | Disable file name generation using metacharacters (globbing).  
set -v | set -o verbose| Prints shell input lines as they are read.  
set -x | set -o xtrace | Print command traces before executing command.  

...

Alternatively, these modes can be specified in the script itself, by adding the desired options to the first line shell declaration. Options can be combined, as is usually the case with UNIX commands:

#!/bin/bash -xv

Answer 8

Type "bash -x" on the command line before the name of the bash script. For instance, to execute foo.sh, type:

bash -x foo.sh

Answer 9

You can execute a bash script in debug mode with the -x option.
This will echo all the commands.

bash -x example_script.sh

# Console output
+ cd /home/user
+ mv text.txt mytext.txt

You can also save the -x option in the script. Just specify the -x option in the shebang.

######## example_script.sh ###################
#!/bin/bash -x

cd /home/user
mv text.txt mytext.txt

##############################################

./example_script.sh

# Console output
+ cd /home/user
+ mv text.txt mytext.txt

Answer 10

Someone above posted:

#!/bin/bash
#function to display commands
exe() { echo "\$ $@" ; "$@" ; }

and this looks promising, but I can't for the life of me figure out what it does. I've googled and searched in the man bash page for "\$" and "$@", and find absolutely nothing.

I understand a function is being created, named "exec()". I understand the curly-brackets mark the beginning and end of the function. I think I understand that the semi-colon marks a "hard return" between a multi-line command, so that '{ echo "\$ $@" ; "$@" ; }' becomes, in essence:

{
echo "\$ $@"
"$@"

}

Can any one give me a brief explanation, or where to find this info, since obviously my google-fu is failing me?

(Without meaning to start a new question on an old thread, my goal is to reroute the output to a file. The "set -x ; [commands] ; set +x" method would work adequately well for me, but I can't figure out how to echo the results to a file instead of the screen, so I was trying to understand this other method in hopes I could use me very poor understanding of redirection/pipes/tee/etc to do the same thing.)

Thanks!

LATER EDIT:

With some tinkering, I believe I figured it out. Here's my equivalent code for what I'm needing:

SCRIPT_LOG="\home\buddy\logfile.txt"
exe () {
  params="$@"                       # Put all of the command-line into "params"
  printf "%s\t$params" "$(date)" >> "$SCRIPT_LOG"   # Print the command to the log file
  $params                           # Execute the command
}

exe rm -rf /Library/LaunchAgents/offendingfile
exe rm -rf /Library/LaunchAgents/secondoffendingfile

The results in the logfile.txt look something like:

Tue Jun  7 16:59:57 CDT 2016  rm -rf /Library/LaunchAgents/offendingfile
Tue Jun  7 16:59:57 CDT 2016  rm -rf /Library/LaunchAgents/secondoffendingfile

Just what I needed. Thanks!

Answer 11

For zsh echo

 setopt VERBOSE

and for debugging

 setopt XTRACE

Answer 12

For csh and tcsh, you can set verbose or set echo (or you can even set both, but it may result in some duplication most of the time).

The verbose option prints pretty much the exact shell expression that you type.

The echo option is more indicative of what will be executed through spawning.

---

http://www.tcsh.org/tcsh.html/Special_shell_variables.html#verbose

http://www.tcsh.org/tcsh.html/Special_shell_variables.html#echo

---

Special shell variables

verbose If set, causes the words of each command to be printed, after history substitution (if any). Set by the -v command line option.

echo If set, each command with its arguments is echoed just before it is executed. For non-builtin commands all expansions occur before echoing. Builtin commands are echoed before command and filename substitution, because these substitutions are then done selectively. Set by the -x command line option.

Answer 13

To allow for compound commands to be echoed, I use eval plus Soth's exe function to echo then run the command. This is useful for piped commands that would otherwise only show none or just the initial part of the piped command.

Without eval:

exe() { echo "\$ $@" ; "$@" ; }
exe ls -F | grep *.txt

Outputs:

$
file.txt

With eval:

exe() { echo "\$ $@" ; "$@" ; }
exe eval 'ls -F | grep *.txt'

Which outputs

$ exe eval 'ls -F | grep *.txt'
file.txt

Answer 14

$ cat exampleScript.sh
#!/bin/bash
name="karthik";
echo $name;

bash -x exampleScript.sh

Output is as follows: