I'm looping over lines in a file. I just need to skip lines that start with "#". How do I do that?
#!/bin/sh
while read line; do
if ["$line doesn't start with #"];then
echo "line";
fi
done < /tmp/myfile
Thanks for any help!
2 Answers
while read line; do
case "$line" in \#*) continue ;; esac
...
done < /tmp/my/input
Frankly, however, it is often clearer to turn to grep:
grep -v '^#' < /tmp/myfile | { while read line; ...; done; }
-
You could also do something too clever with
expror suffix removal (e.g.,[ -z "${line%%#*}" ]), but these would be equally or less readable than thecaseoption, I think.– pilcrowCommented Sep 19, 2012 at 4:43 -
2To also strip lines where whitespace (only) precedes
#, usegrep -v '^\s*#' < /tmp/myfileinstead - this is in line with thecasesolution, given thatreadstrips leading and trailing whitespace. Commented Sep 19, 2012 at 4:59 -
4Another option (if for some reason someone wanted to avoid
grep) might beif [[ $line =~ ^# ]]; then continue; fi. Commented Sep 19, 2012 at 6:50 -
2The grep solution won't work if the while loop needs to modify variables in the current shell, as the loop runs in a subshell (unless bash 4.2 is available and
set -o lastpipeis used). Other shells may run the while loop in the current shell by default.– chepnerCommented Sep 19, 2012 at 12:32 -
8
This is an old question but I stumbled upon this problem recently, so I wanted to share my solution as well.
If you are not against using some python trickery, here it is:
Let this be our file called "my_file.txt":
this line will print
this will also print # but this will not
# this wont print either
# this may or may not be printed, depending on the script used, see below
Let this be our bash script called "my_script.sh":
#!/bin/sh
line_sanitizer="""import sys
with open(sys.argv[1], 'r') as f:
for l in f.read().splitlines():
line = l.split('#')[0].strip()
if line:
print(line)
"""
echo $(python -c "$line_sanitizer" ./my_file.txt)
Calling the script will produce something similar to:
$ ./my_script.sh
this line will print
this will also print
Note: the blank line was not printed
If you want blank lines you can change the script to:
#!/bin/sh
line_sanitizer="""import sys
with open(sys.argv[1], 'r') as f:
for l in f.read().splitlines():
line = l.split('#')[0]
if line:
print(line)
"""
echo $(python -c "$line_sanitizer" ./my_file.txt)
Calling this script will produce something similar to:
$ ./my_script.sh
this line will print
this will also print
-i, it will useinteractive_comments.