How to make bash scripts print out every command before it executes?

Question

For example, I have a simple bash file

#!/bin/bash
cd ~/hello
ls

How can I make it display every command before executing it? Just the opposite effect of "@echo off" in windows batch scripting.

Solution 1

bash -x script

or

set -x

in the script.

You can unset the option again with set +x. If you just want to do it for a few commands you can use a subshell: `(set -x; command1; command; ...;)

Solution 2

These also work:

set -v

or

#!/bin/bash -v

But -v doesn't print the PS4 string before each script line and it doesn't trace the steps of a "for" statement (for example) individually. It does echo comments while -x doesn't.

Here's an example of the output using -v:

#!/bin/bash -v
# this is a comment
for i in {1..4}
do
    echo -n $i
done
1234echo

echo hello
hello

Here's the result of the same script with -x:

+ for i in '{1..4}'
+ echo -n 1
1+ for i in '{1..4}'
+ echo -n 2
2+ for i in '{1..4}'
+ echo -n 3
3+ for i in '{1..4}'
+ echo -n 4
4+ echo

+ echo hello
hello

Note that I included "echo -n" to add emphasis to the differences between -v and -x. Also, -v is the same as "-o verbose", but the latter seems not to work as part of a shebang.

Solution 3

This should also work:

#!/bin/bash -x
cd ~/hello
ls

Solution 4

This should work:

set -o verbose #echo on
...
set +o verbose #echo off

Solution 5

set -o xtrace and set +o xtrace are your friends (it is more verbose, than -o verbose, and the output goes to STDERR, as opposed to verbose, which seems to log to STDOUT).

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Comments

[mkobit]

For those looking for what the set options are, you can find them on this man page.

[sobi3ch]

You can simply extend shebang like this #!/bin/bash -x

[Scott Pack]

I have always used this to great effect. The output looks a little dirtier than you might first expect.

[Ape-inago]

Great explanation! without doing any research, it looks to me like Verbose and eXplicit are what those two letters stand for.

[Steven Parkes]

I think -x is closer to eXecute.

[Walter Tross]

By setting PS4 you can tweak the prompt of -x. E.g.: PS4='Line $LINENO @ $(date +%s.%N): ' bash -x script (date will slow it down, though)

[Eugene Pankov]

-x has nothing to with echoing in Python