I have header files that have a lot of #define statements like: #define GPSVersion 0x000;
I would like to write a Bash script to extract the text GPSVersion into a file. But how do I use grep to do that? I can find the pattern #define but how do I find the text following #define ? Thanks.
echo "#define GPSVersion 0x000;" | awk '{print $2}'
cat file.h | grep ^'#define' | awk '{print $2}'
#define in comments. Use '^#define to print only lines that start with #define. Using cat starts an extra unnecessary process. grep $PATTERN < $FILE is more efficient. Since you're always printing the second field, awk is overkill; cut is far more efficient.
Try this one-liner that uses Perl instead of grep:
perl -ne 'print "$1\n" if $_ =~ /#define \b(\w+?)\b.*/' < header.h
where header.h is the file that has #define GPSVersion 0x000 in it.
Steps:
catyour file. (an echo in sample)Command:
echo "#define GPSVersion 0x000;" | grep ^"#defin" | cut -d" " -f2
GPSVersionGPSVersion and that the OP wanted to collect the actual version numbers. I've updated my answer accordingly.I think this works for you:
grep -r '#define[[:space:]]*GPSVERSION[[:space:]].*' . | tr -s ' \t' '\t' | cut -f 3
grep -r : scans ALL the files in the specified directory and subdirectories
'#define[[:space:]]*GPSVERSION[[:space:]].*' : is a regexp that matches all the #define directives, ignoring the whitespacing and considering only #defines that have a value assigned to them.
Grep prints its output, then the output is passed to tr -s ' \t' '\t' which convert blanks to something suitable for cut
Finally cut -f3 prints only the desired value of the define.
It works well except: comment defines (//#define) and filenames with spaces in them.
$find /path/to/root/of/source/tree -name '*.h' |
xargs grep '^#define.*GPSVersion' | cut -d' ' -f 2
Explanation:
The find command will print all files in the source tree whose names end in .h -- that is, all of your header files.
The xargs command passes the file names to grep, which will print all the lines that begin with #define, followed by one or more characters, followed by GPSVersion.
The cut command will print the 2nd field (the text that's being #defined), using the space characters as delimiters between fields.