On Mon, Nov 15, 2021 at 12:40:22AM +0800, 積丹尼 Dan Jacobson wrote:
> Man page says:
> -v Print shell input lines as they are read.
> -x Print commands and their arguments as they are executed.
> Perhaps mention that -x and -vx give the same results, often or always.
> GNU bash, version 5.1.8
They're extremely different.
-v only prints lines when bash reads them from its script. NOT when
bash executes them. It prints the line exactly as it's read, without
any expansions.
-x prints commands that bash EXECUTES. Arguments are expanded, and
redirections are not shown.
You almost never want -v. It's pretty useless.
unicorn:~$ cat foo
#!/bin/bash
for i in {1..10}; do
: stuff
done
unicorn:~$ bash -v foo
#!/bin/bash
for i in {1..10}; do
: stuff
done
unicorn:~$ bash -x foo
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
+ for i in {1..10}
+ : stuff
In the "bash -v foo" output, you can see each line of the script as it
gets read. Bash reads the entire for loop at once, then parses it, then
runs it. The -v output shows you NOTHING after the loop has been read.
The -x output shows you each iteration of the loop.
