So, I have this assignment which requires me to delete a certain line from a .dat file. Now my file is basically a phone book. I have a Bash script that adds the ID, name, last name, phone number, address, etc., to the .dat file. Now one of the flags is supposed to be -delete and it takes the parameter id. So, basically I need to implement the function where I'd put ./phonebook.sh -delete -id 7 and it would delete the row where the id is 7.
I tried using sed and awk, but nothing is working and it's frustrating. My current code for that short script (delete.sh) is:
id=$1
sed "/$id/d" phonebook.dat
Try this:
On Mac:
sed -i '' -e "/$id/d" phonebook.dat
Otherwise:
sed -i -e "/$id/d" phonebook.dat
By default, sed will output the results to stdout. So, your command was working, but the output wasn't going back into the file. The -i flag says that the file should be replaced with the results. -i is also meant to backup the original file. For example:
sed -i .bk -e "/$id/d" phonebook.dat
The above will create a copy of the original called: phonebook.dat.bk. However, to do in place replacement without a backup, you can specify no value for -i. On the MAC, sed really really really wants a value, so you can pass it an empty string ( making sure there is a space between the -i and the empty quotes ).
I'm making some assumptions because I don't know what the format of your dat file is. I'll assume that the id field is the first field and the file is comma delimited. If I'm wrong, you should be able to modify the below to fit your needs.
I personally like to use grep -v for this problem. From the --help:
-v, --invert-match select non-matching lines
Running this will output every line of a file that does not match your pattern.
id="$1"
grep -v "^${id}," phonebook.dat > phonebook.temp
mv phonebook.temp phonebook.dat
The pattern consists of
^: Beginning of the line
${id}: Your variable
,: Our assumed delimiter
The reason for specifying the beginning of the line to the first delimiter is to avoid deleting entries where the entered id ($1) is a substring of other ids. You wouldn't want to enter 22 and delete id 22 as well as id 122.
Related
I have output file that can be read by a visualizing tool, the problem is that at the beginning of each line there is one space. Because of this the visualizing tool isn't able to recognize the scripts and, hence crashing. When I manually remove the first column of spaces, it works fine. Is there a way to remove the 1st empty column of spaces using bash command
What I want is to remove the excess column of empty space like shown in this second image using a bash command
At present I use Vim editor to remove the 1st column manually. But I would like to do it using a bash command so that I can automate the process. My file is not just full of columns, it has some independent data line
Using cut or sed would be two simple solutions.
cut
cut -c2- file > file.cut && mv file.cut file
cut cannot modify a file, therefore you need to redirect its output to a different file and then overwrite the old file with the new file.
sed
sed -i 's/^.//' file
-i modifies the file in-place.
I would use
sed -ie 's/^ //' file
to just remove spaces (in case a line does not contain it)
I'm quite new to bash scripting. I have a script where I want to extract part of the value of a particular line in a separate config file and then use that value as a variable in the script.
For example:
Line 75 in a file named config.cfg
"ssl_cert_location=/etc/ssl/certs/thecert.cer"
I want just the value at the end of "thecert.cer" to then use in the script. I've tried awk and various uses of grep but I can't quite get just the name of the certificate.
Any help would be appreciated. Thanks
These are some examples of the commands I ran:
awk -F "/" '{print $4}' config.cfg
grep -o *.cer config.cfg
Is this possible to extract the value on that line and then edit the output so it just contains the name of the certificate file?
This is a pure Bash version of the basic functionality of basename:
cert=${line##*/}
which removes everything up to and including the final slash. It presupposes that you've already read the line.
Or, using sed:
cert=$(sed -n '75s/^.*\///p' filename)
or
cert=$(sed -n '/^ssl_cert_location=/s/^.*\///p' filename)
This gets the specified line based on the line number or the setting name and replaces everything up to and including the final slash with nothing. It ignores all other lines in the file (unless the setting is repeated in the case of the text match version). The text match version is better because it works no matter what line number the setting is on.
grep uses regular expressions (as does sed). The grep command in your command appears to have a glob expression which won't work. One way to use grep (GNU grep) is to use the PCRE feature (Perl Compatible Regular Expressions):
cert=$(grep -Po '^ssl_cert_location=.*/\K.*' filename)
This works similarly to the sed command.
I have anchored the regular expressions to the beginning of the line. If there may be leading white spaces (the line may be indented), change the regex so it looks something like this:
^[[:space:]]*ssl_cert_location=
which works for both indented and unindented lines.
There are many variants, but a simple one that comes to mind with grep is first getting the line, then matching only non-slashes at the end of the line:
<config.cfg grep '^ssl_cert_location=' | grep -o '[^/]*$'
Why didn't your grep command (grep -o *.cer config.cfg) work? Becasue *.cer is a shell glob pattern and will be expanded by the shell to matching file names, even before the grep process is even started. If there are no matching files, it will be passed verbatim, but * in regular expressions is a quantifier which needs a preceeding expression. . in regex is "match any single character". So what you wanted is probably grep -o '.*\.cer', but .* matches anything, including slashes.
An awk solution would look like the following:
awk -F/ '/^ssl_cert_location=/{print $NF}' config.cfg
It uses "/" as separator, finds only lines starting with "ssl_cert_location" and then prints the last (NF) field in from this line.
Or an equivalent sed solution, which matches the same line and then deletes everything including the last slash:
sed -n '/^ssl_cert_location=/s#^.*/##p' config.cfg
To store the output of any command in a variable, use command substitution:
var="$(command with arguments)"
I have a file BookDB.txt which stores information in the following manner :
C++ for dummies:Jared:10.67:4:5
Java for dummies:David:10.45:3:6
PHP for dummies:Sarah:10.47:2:7
Assuming that during runtime, the scipt asks the user for the title he wants to delete. This is then stored in the TITLE variable. How do I then delete the line containing the string in question? I've tried the following command but to no avail :
sed '/$TITLE/' BookDB.txt >> /dev/null
You can for example do:
$ title="C++ for dummies"
$ sed -i "/$title/d" a
$ cat a
**Java for dummies**:David:10.45:3:6
**PHP for dummies**:Sarah:10.47:2:7
Note few things:
Double quotes in sed are needed to have you variable expanded. Otherwise, it will look for the fixed string "$title".
With -i you make in-place replacement, so that your file gets updated once sed has performed.
d is the way to indicate sed that you want to delete such matching line.
Your command should be,
sed "/$TITLE/d" file
To save the changes, you need to add -i inline edit parameter.
sed -i "/$TITLE/d" file
For variable expansion in sed, you need to put the code inside double quotes.
I am trying to remove 2 lines from all my Javascript files on my Linux shared hosting. I wanted to do this without writing a script as I know this should be possible with sed. My current attempt looks like this:
find . -name "*.js" | xargs sed -i ";var
O0l='=sTKpUG"
The second line is actually longer than this but is malicious code so I have not included it here. As you guessed my server has been hacked so I need to clean up all these JavaScript files.
I forgot to mention that the output I am getting at the moment is:
sed: -e expression #1, char 4: expected newer version of sed
The 2 lines are just as follows consecutively:
;var
O0l='=sTKpUG
except that the second line is longer, but the rest of the second line should not influence the command.
He meant removing two adjacent lines.
you can do something like this, remember to backup your files.
find . -name "*.js" | xargs sed -i -e "/^;var/N;/^;var\nO0l='=sTKpUG/d"
Since sed processes input file line by line, it does not store the newline '\n' character in its buffer, so we need to tell it by using flag /N to append the next line, with newline character.
/^;var/N;
Then we do our pattern searching and deleting.
/^;var\nO0l='=sTKpUG/d
It really isn't clear yet what the two lines look like, and it isn't clear if they are adjacent to each other in the JavaScript, so we'll assume not. However, the answer is likely to be:
find . -name "*.js" |
xargs sed -i -e '/^distinctive-pattern1$/d' -e '/^alternative-pattern-2a$/d'
There are other ways of writing the sed script using a single command string; I prefer to use separate arguments for separate operations (it makes the script clearer).
Clearly, if you need to keep some of the information on one of the lines, you can use a search pattern adjusted as appropriate, and then do a substitute s/short-pattern// instead of d to remove the short section that must be removed. Similarly with the long line if that's relevant.
I use DJing software on linux (xwax) which uses a 'scanning' script (visible here) that compiles all the music files available to the software and outputs a string which contains a path to the filename and then the title of the mp3. For example, if it scans path-to-mp3/Artist - Test.mp3, it will spit out a string like so:
path-to-mp3/Artist - Test.mp3[tab]Artist - Test
I have tagged all my mp3s with BPM information via the id3v2 tool and have a commandline method for extracting that information as follows:
id3v2 -l name-of-mp3.mp3 | grep TBPM | cut -D: -f2
That spits out JUST the numerical BPM to me. What I'd like to do is prepend the BPM number from the above command as part of the xwax scanning script, but I'm not sure how to insert that command in the midst of the script. What I'd want it to generate is:
path-to-mp3/Artist - Test.mp3[tab][bpm]Artist - Test
Any ideas?
It's not clear to me where in that script you want to insert the BPM number, but the idea is this:
To embed the output of one command into the arguments of another, you can use the "command substitution" notation `...` or $(...). For example, this:
rm $(echo abcd)
runs the command echo abcd and substitutes its output (abcd) into the overall command; so that's equivalent to just rm abcd. It will remove the file named abcd.
The above doesn't work inside single-quotes. If you want, you can just put it outside quotes, as I did in the above example; but it's generally safer to put it inside double-quotes (so as to prevent some unwanted postprocessing). Either of these:
rm "$(echo abcd)"
rm "a$(echo bc)d"
will remove the file named abcd.
In your case, you need to embed the command substitution into the middle of an argument that's mostly single-quoted. You can do that by simply putting the single-quoted strings and double-quoted strings right next to each other with no space in between, so that Bash will combine them into a single argument. (This also works with unquoted strings.) For example, either of these:
rm a"$(echo bc)"d
rm 'a'"$(echo bc)"'d'
will remove the file named abcd.
Edited to add: O.K., I think I understand what you're trying to do. You have a command that either (1) outputs out all the files in a specified directory (and any subdirectories and so on), one per line, or (2) outputs the contents of a file, where the contents of that file is a list of files, one per line. So in either case, it's outputting a list of files, one per line. And you're piping that list into this command:
sed -n '
{
# /[<num>[.]] <artist> - <title>.ext
s:/\([0-9]\+.\? \+\)\?\([^/]*\) \+- \+\([^/]*\)\.[A-Z0-9]*$:\0\t\2\t\3:pi
t
# /<artist> - <album>[/(Disc|Side) <name>]/[<ABnum>[.]] <title>.ext
s:/\([^/]*\) \+- \+\([^/]*\)\(/\(disc\|side\) [0-9A-Z][^/]*\)\?/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t\1\t\6:pi
t
# /[<ABnum>[.]] <name>.ext
s:/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t\t\2:pi
}
'
which runs a sed script over that list. What you want is for all of the replacement-strings to change from \0\t... to \0\tBPM\t..., where BPM is the BPM number computed from your command. Right? And you need to compute that BPM number separately for each file, so instead of relying on seds implicit line-by-line looping, you need to handle the looping yourself, and process one line at a time. Right?
So, you should change the above command to this:
while read -r LINE ; do # loop over the lines, saving each one as "$LINE"
BPM=$(id3v2 -l "$LINE" | grep TBPM | cut -D: -f2) # save BPM as "$BPM"
sed -n '
{
# /[<num>[.]] <artist> - <title>.ext
s:/\([0-9]\+.\? \+\)\?\([^/]*\) \+- \+\([^/]*\)\.[A-Z0-9]*$:\0\t'"$BPM"'\t\2\t\3:pi
t
# /<artist> - <album>[/(Disc|Side) <name>]/[<ABnum>[.]] <title>.ext
s:/\([^/]*\) \+- \+\([^/]*\)\(/\(disc\|side\) [0-9A-Z][^/]*\)\?/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t'"$BPM"'\t\1\t\6:pi
t
# /[<ABnum>[.]] <name>.ext
s:/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t'"$BPM"'\t\t\2:pi
}
' <<<"$LINE" # take $LINE as input, rather than reading more lines
done
(where the only change to the sed script itself was to insert '"$BPM"'\t in a few places to switch from single-quoting to double-quoting, then insert the BPM, then switch back to single-quoting and add a tab).