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

I use a function to echo and run the command:

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

exe echo hello world

Which outputs

$ echo hello world
hello world

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 4

You can also toggle this for select lines in your script by wrapping them in set -x and set +x, for example,

#!/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 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

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 7

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
$

Answer 8

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 9

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 10

Combining all the answers I found this to be the best, simplest

#!/bin/bash
# https://stackoverflow.com/a/64644990/8608146
exe(){
    set -x
    "$@"
    { set +x; } 2>/dev/null
}
# example
exe go generate ./...

{ set +x; } 2>/dev/null from https://stackoverflow.com/a/19226038/8608146

If the exit status of the command is needed, as mentioned here

Use

{ STATUS=$?; set +x; } 2>/dev/null

And use the $STATUS later like exit $STATUS at the end

A slightly more useful one

#!/bin/bash
# https://stackoverflow.com/a/64644990/8608146
_exe(){
    [ $1 == on  ] && { set -x; return; } 2>/dev/null
    [ $1 == off ] && { set +x; return; } 2>/dev/null
    echo + "$@"
    "$@"
}
exe(){
    { _exe "$@"; } 2>/dev/null
}

# examples
exe on # turn on same as set -x
echo This command prints with +
echo This too prints with +
exe off # same as set +x
echo This does not

# can also be used for individual commands
exe echo what up!

Answer 11

For zsh, echo

setopt VERBOSE

And for debugging,

setopt XTRACE

Answer 12

To allow for compound commands to be echoed, I use eval plus Soth's exe function to echo and 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 13

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 14

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

bash -x exampleScript.sh

Output is as follows:

Answer 15

Following the answer of Soth.

It is possible to create a markdown output without highlight (no language given)

set -x
exe() { echo "\`\$\$  ${@/eval/} \`" ; "$@" ; }

script

set -x
exe() { echo "\`\$\$  ${@/eval/} \`" ; "$@" ; }
echo
echo -----------------------------------------------------------
echo # Setup
echo Lets take a random keyframe from in.mp4:
echo
exe eval "kfn=20"
echo
echo "kf=\$(ffprobe -v error -select_streams v -show_frames -print_format csv in.mp4 | grep 'frame,video,0,1' | head -$kfn | tail -1 | perl -pe 's|frame,video,0,1,.*?,(.*?),.*|\1|') "
exe eval "kf=$(ffprobe -v error -select_streams v -show_frames -print_format csv in.mp4 | grep 'frame,video,0,1' | head -$kfn | tail -1 | perl -pe 's|frame,video,0,1,.*?,(.*?),.*|\1|') "
echo
echo Lets select keyframe at $kf. Here are the timestamps of the all the frames from in.mp4 around this keyframe.
echo
exe eval "ffprobe -v error -select_streams v -show_frames -print_format csv in.mp4  | perl -pe 's|frame,video,0,(.*?),.*?,(.*?),.*|\2  \1|' | perl -pe 's|(.*?)  1|\1\tKF|' |  perl -pe 's|(.*?)  0|\1|' |grep -A 5 -B 5 --color $kf"
echo
echo Lets compare 2 methods of split: actual losslesscut 3.53.0 and another one
echo

Output

---

Lets take a random keyframe from in.mp4:

$$ kfn=20

kf=$(ffprobe -v error -select_streams v -show_frames -print_format csv in.mp4 | grep 'frame,video,0,1' | head -20 | tail -1 | perl -pe 's|frame,video,0,1,.?,(.?),.*|\1|')

$$ kf=3.803792

Lets select keyframe at 3.803792. Here are the timestamps of the all the frames from in.mp4 around this keyframe.

$$ ffprobe -v error -select_streams v -show_frames -print_format csv in.mp4 | perl -pe 's|frame,video,0,(.*?),.*?,(.*?),.*|\2 \1|' | perl -pe 's|(.*?) 1|\1\tKF|' | perl -pe 's|(.*?) 0|\1|' |grep -A 5 -B 5 --color 3.803792

3.720375
3.737083
3.753750
3.770417
3.787125
**3.803792**   KF
3.820500
3.837167
3.853833
3.870542
3.887208

Answer 16

If you want to log only specific commands, rather than every single line, set -x is somewhat difficult to use. But you can use this function to print any command, prefixed with $ :

function run() {
    echo -n '$'  # Print $ without a newline.
    for arg in "$@"; do
      printf " %q" "$arg"  # Print $arg, properly escaped.
    done
    echo  # Print a newline.
    "$@"
}

Usage:

run ls /full/path/to/some/dir

Using printf with the %q format specifier makes sure that the output is printed in a way suitable for copying and pasting into a shell, even in the presence of spaces or other special characters. It seems to escape spaces using \ rather than adding quotes, but the output does correctly represent what's actually being run.