I have the following code:
#!/bin/bash
for f in `find . ! -type d`;
do
line=`grep -i 'todo' $f | sed 's/^[ \t]*//'`
if [ $line ]; then
echo "$f:"
echo "$line"
fi
done
but the condition is not working as I would expect it, I need it to only work if something other than an empty string (or nothing) is returned by the command.
As Alberto pointed out, it's common to use -n to check to see if a string has a non-zero length, but in the case where the string may be empty or contain only whitespace, you'll want to quote the variable:
if [ -n "$line" ] # ...
Similarly, you can check to see if it has a zero length with -z:
if [ -z "$line" ] # ...
Negation is also supported when it makes more sense:
if [ ! -z "$line" ] # ...
Edit: And since you're using bash, you can actually use some other nice features such as:
[[ expr ]]), and[[ cat =~ ca[bat] ]])See the conditional constructs section in man bash for more information.
Some ideas:
$f in the grep line to deal with files with spaces in their names.-f rather than ! -d, otherwise your find may hang on fifos.\t escape didn't work as a tab match, it consumed a leading t in a test case file line, so I just inserted a raw tab character in the script instead.A slight variation on your script would then be:
find . -type f | while read f
do
# raw tab in here ------------------- v
line=`grep -i 'todo' "$f" | sed 's/^[ ]*//'`
if [[ $line ]]; then
echo "$f:"
echo "$line"
fi
done
read builtin supports -r (raw mode) and -d (change delimiter), this should handle any bizarre filenames you throw at it: find . -type f -print0 | while IFS="" read -r -d $'\000' f; do ... (note that the IFS setting only applies to the read command, not to the contents of the loop... except on a few buggy shells).The old school notation (usable with archaic things like Bourne Shell, and not so archaic things such as Korn shell) is:
for f in `find . ! -type d`
do
line=`grep -i 'todo' $f | sed 's/^[ \t]*//'`
if [ -n "$line" ]
then
echo "$f:"
echo "$line"
fi
done
You could speed up the overall processing, though, by using:
find . ! -type d -print0 | xargs -0 grep -i 'todo' /dev/null |
perl -p -e '($name) = split /:/;
if ($saved ne $name) { $saved = $name; print "$name:\n"; }
s/^$name:\s*//;'
The find is modified to handle spaces in names; the xargs also handles spaces in names, and runs the grep command on /dev/null plus some files - which ensures that matching lines are preceded by the file name. The perl script splits the line at the first colon - so file names containing colons are not good news. It compares that name with what it had saved before; if they are different, then it prints out the new name, colon and newline to give you the file heading. Then it removes the file name and trailing spaces before (automatically) printing the line. (Don't use '-w' with Perl; it complains about $saved being uninitialized. If you must (it is good practice), add BEGIN { $saved = ""; }.)
This is likely to perform better than the shell loop because it invokes grep just a few times rather than once per file, and doesn't invoke the sed at all (instead of once per file).
if [ -n $line ]
Checks if $line is empty string.
This is one I like:
if [ ${PIPESTATUS[0]} -eq 0 ]; then echo lines found; fi
it takes the exit status of the grep. man page tells:
EXIT STATUS
Normally, the exit status is 0 if selected lines are found and 1 otherwise.
Use POSIX character classes if you can:
# cf. http://en.wikipedia.org/wiki/Regular_expression#POSIX_character_classes
sed 's/[[:blank:]]/-wasTabOrSpace-/g' <<< $'abc\t def'
Since we have a subshell because of the `...` or $(...) construct respectively, we can exit the subshell like any other (parent) shell with a specified PIPESTATUS-based exit code! :-)
# simple test
var="$(echooo hello 2>/dev/null | cat)"
echo ${PIPESTATUS[0]} # 0
var="$(echooo hello 2>/dev/null | cat; exit ${PIPESTATUS[0]})"
echo ${PIPESTATUS[0]} # 127
findcommand:touch "very odd"; for i in `find .`; do echo $i; donewill give surprising results...