#!/bin/sed -f
s/","/|/g; # global change of "," to bar
# do some more stuff
#s/|/","/g; # global change of bar back to ","
#---end of script---
The above script removes the 2nd field from a CSV, and clears out quotes and such. I didn't include most of the script because it's not pertinent to the question.
The script is saved in the file fix.sh.
I can run it on a file like this:
$ ./fix.sh <myfile.txt >outputfile.txt
And it works great.
But I want it to replace in file. This doesn't work:
$ ./fix.sh <myfile.txt >myfile.txt
It results in an empty myfile.txt.
This doesn't work either:
$ ./fix.sh myfile.txt
I tried finding some documentation on sed bash scripts but didn't find anything to help me.
I'm sure the answer is simple, I just can't find it. Thanks for your help.
EDIT: I should have mentioned that this is running on a CentOS 6 machine.
Full script is below. Its overall result is to remove field#2 and strip quotes.
#!/bin/sed -nf
# adapted from http://www.linuxtopia.org/online_books/linux_tool_guides/the_sed_faq/sedfaq4_005.html
s/","/|/g; # global change of "," to bar
s/^"//;
s/"$//;
s/^\([^|]*\)|[^|]*|/\1|/; # delete 2nd field contents
s/||/|/; # change || to |
s/ //g; # remove spaces
s/|/,/g;
#s/|/","/g; # global change of bar back to ","
#---end of script---
If your sed supports -i option then you can run your script like this:
./fix.sh -i myfile.txt
-i option of sed does the in-file substitutions.
If your version of sed does not support the -i option then you can do the following which is pretty much the same thing that -i does behind the scene:
./fix.sh myfile.txt > temp && mv temp myfile.txt
Why redirecting to the same file doesn't work?
The reason is that the redirection opens the file for writing and ends up clearing any existing contents. sed then tries to read this empty file, and does nothing. The file is then closed and there by you get an empty file.
Related
I would like to run a find and replace on an HTML file through the command line.
My command looks something like this:
sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html > index.html
When I run this and look at the file afterward, it is empty. It deleted the contents of my file.
When I run this after restoring the file again:
sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html
The stdout is the contents of the file, and the find and replace has been executed.
Why is this happening?
When the shell sees > index.html in the command line it opens the file index.html for writing, wiping off all its previous contents.
To fix this you need to pass the -i option to sed to make the changes inline and create a backup of the original file before it does the changes in-place:
sed -i.bak s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html
Without the .bak the command will fail on some platforms, such as Mac OSX.
An alternative, useful, pattern is:
sed -e 'script script' index.html > index.html.tmp && mv index.html.tmp index.html
That has much the same effect, without using the -i option, and additionally means that, if the sed script fails for some reason, the input file isn't clobbered. Further, if the edit is successful, there's no backup file left lying around. This sort of idiom can be useful in Makefiles.
Quite a lot of seds have the -i option, but not all of them; the posix sed is one which doesn't. If you're aiming for portability, therefore, it's best avoided.
sed -i 's/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g' index.html
This does a global in-place substitution on the file index.html. Quoting the string prevents problems with whitespace in the query and replacement.
use sed's -i option, e.g.
sed -i bak -e s/STRING_TO_REPLACE/REPLACE_WITH/g index.html
To change multiple files (and saving a backup of each as *.bak):
perl -p -i -e "s/\|/x/g" *
will take all files in directory and replace | with x
this is called a “Perl pie” (easy as a pie)
You should try using the option -i for in-place editing.
Warning: this is a dangerous method! It abuses the i/o buffers in linux and with specific options of buffering it manages to work on small files. It is an interesting curiosity. But don't use it for a real situation!
Besides the -i option of sed
you can use the tee utility.
From man:
tee - read from standard input and write to standard output and files
So, the solution would be:
sed s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html | tee | tee index.html
-- here the tee is repeated to make sure that the pipeline is buffered. Then all commands in the pipeline are blocked until they get some input to work on. Each command in the pipeline starts when the upstream commands have written 1 buffer of bytes (the size is defined somewhere) to the input of the command. So the last command tee index.html, which opens the file for writing and therefore empties it, runs after the upstream pipeline has finished and the output is in the buffer within the pipeline.
Most likely the following won't work:
sed s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html | tee index.html
-- it will run both commands of the pipeline at the same time without any blocking. (Without blocking the pipeline should pass the bytes line by line instead of buffer by buffer. Same as when you run cat | sed s/bar/GGG/. Without blocking it's more interactive and usually pipelines of just 2 commands run without buffering and blocking. Longer pipelines are buffered.) The tee index.html will open the file for writing and it will be emptied. However, if you turn the buffering always on, the second version will work too.
sed -i.bak "s#https.*\.com#$pub_url#g" MyHTMLFile.html
If you have a link to be added, try this. Search for the URL as above (starting with https and ending with.com here) and replace it with a URL string. I have used a variable $pub_url here. s here means search and g means global replacement.
It works !
The problem with the command
sed 'code' file > file
is that file is truncated by the shell before sed actually gets to process it. As a result, you get an empty file.
The sed way to do this is to use -i to edit in place, as other answers suggested. However, this is not always what you want. -i will create a temporary file that will then be used to replace the original file. This is problematic if your original file was a link (the link will be replaced by a regular file). If you need to preserve links, you can use a temporary variable to store the output of sed before writing it back to the file, like this:
tmp=$(sed 'code' file); echo -n "$tmp" > file
Better yet, use printf instead of echo since echo is likely to process \\ as \ in some shells (e.g. dash):
tmp=$(sed 'code' file); printf "%s" "$tmp" > file
And the ed answer:
printf "%s\n" '1,$s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g' w q | ed index.html
To reiterate what codaddict answered, the shell handles the redirection first, wiping out the "input.html" file, and then the shell invokes the "sed" command passing it a now empty file.
I was searching for the option where I can define the line range and found the answer. For example I want to change host1 to host2 from line 36-57.
sed '36,57 s/host1/host2/g' myfile.txt > myfile1.txt
You can use gi option as well to ignore the character case.
sed '30,40 s/version/story/gi' myfile.txt > myfile1.txt
With all due respect to the above correct answers, it's always a good idea to "dry run" scripts like that, so that you don't corrupt your file and have to start again from scratch.
Just get your script to spill the output to the command line instead of writing it to the file, for example, like that:
sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html
OR
less index.html | sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g
This way you can see and check the output of the command without getting your file truncated.
in my script i edit a file by using "sed":
sed -i -e /NumberOfEntries=*/d "$playlist_name" > /dev/null # deletes "NumberOfEntries"-line
sed -i -e '/^$/d' "$playlist_name" > /dev/null # deletes all empty lines
This works just fine but while execution (and shortly after) there are one or two temporary files named something like "sedJjHEt2" (the string after sed changes everytime i run the script). The file is marked with a lock and red X-Symbol.
Is there a way to turn this off or am I missing something that I need to adjust? Or is this because of the "-i" Option?
Thanks in advance!
Because of the "-i" Option.
once you use "-i", sed will create a temporary, and then replace the original file with the temporary file.
I am trying to script a way of removing hosts from the hostgroup file in Nagios Core.
The format of the hostgroup file is:
server1,server2,server3,server4
When removing a server, I need to be able to not only remove the server, but also the comma that follows it. So in my example above, if I am removing server2, the file would result as follows
server1,server3,server4
So I have googled and tested the following which works to remove server2 and a comma after it (I don't know what the b is used for exactly)
sed -i 's/\bserver2\b,//g' myfile
What I want to be able to do is to feed a list of hostnames to a small script to remove a bunch of hosts (and their following comma) with something similar to the following. The problem lies in that placing a variable like $x breaks the script so that nothing happens.
#!/bin/ksh
for x in `cat /tmp/list`
do
sed -i 's/\b${x}\b,//g' myfile
done
I think I am very close on a solution here, but could use a little help. Thanks much in advance for your kind assistance.
Using single quotes tells the shell not to replace the ${x} - it turns off variable interpolation if you want to google for it.
https://www.tldp.org/LDP/abs/html/quotingvar.html. So use double quotes around the sed replacement string instead:
while read -r x; do sed -i "s/\b${x},\b//g" myfile; done < /tmp/list
But since the last field won't have a comma after it, might be a good idea to run two sed commands, one looking for \bword,\b and the other for ,word$ - where \b is a word boundary and $ is the end of line.
while read -r x; do sed -i "s/\b${x},\b//g" myfile; sed -i "s/,${x}$//" myfile ; done < /tmp/list
One other possible boundary condition - what if you have just server2 on a line by itself and that's what you're trying to delete? Perhaps add a third sed, but this one will leave a blank line behind which you might want to remove:
while read -r x
do
sed -i "s/\b${x},\b//g" myfile # find and delete word,
sed -i "s/,${x}$//" myfile # find and delete ,word
sed -i "s/^${x}$//" myfile # find word on a line by itself
done < t
This works quite nicely:
#!/bin/bash
IN_FILE=$1
shift; sed -i "s/\bserver[$#],*\b//g" $IN_FILE; sed -i "s/,$//g" $IN_FILE
if you invoke it like ./remove_server.sh myfile "1 4" for your example file containing server1,server2,server3,server4, you get the following output:
server2,server3
A quick explanation of what it does:
shift shifts the arguments down by one (making sure that "myfile" isn't fed into the regex)
First sed removes the server with the numbers supplied as arguments in the string (e.g. "1 4")
Second sed looks for a trailing comma and removes it
The \b matches a word boundary
This is a great resource for learning about and testing regex: https://regex101.com/r/FxmjO5/1. I would recommend you check it out and use it each time you have a regex problem. It's helped me on so many occasions!
An example of this script working in a more general sense:
I tried it out on this file:
# This is some file containing server info:
# Here are some servers:
server2,server3
# And here are more servers:
server7,server9
with ./remove_server.sh myfile "2 9" and got this:
# This is some file containing info:
# Here are some servers:
server3
# And here are more servers:
server7
Pretty sure there is a pure sed solution for this but here is a script.
#!/usr/bin/env bash
hosts=()
while read -r host; do
hosts+=("s/\b$host,\{,1\}\b//g")
done < /tmp/list
opt=$(IFS=';' ; printf '%s' "${hosts[*]};s/,$//")
sed "$opt" myfile
It does not run sed line-by-line, but only one sed invocation. Just in case, say you have to remove 20+ pattern then sed will not run 20+ times too.
Add the -i if you think the output is ok.
Using perl and regex by setting the servers to a regex group in a shell variable:
$ remove="(server1|server4)"
$ perl -p -e "s/(^|,)$remove(?=(,|$))//g;s/^,//" file
server2,server3
Explained:
remove="(server1|server4)" or "server1" or even "server."
"s/(^|,)$remove(?=(,|$))//g" double-quoted to allow shell vars, remove leading comma, expected to be followed by a comma or the end of string
s/^,// file remove leading comma if the first entry was deleted
Use the -i switch for infile editing.
bash script that reads the servers to remove from standard input, one per line, and uses perl to remove them from the hostfile (Passed as the first argument to the script):
#!/usr/bin/env bash
# Usage: removehost.sh hostgroupfile < listfile
mapfile -t -u 0 servers
IFS="|"
export removals="${servers[*]}"
perl -pi -e 's/,?(?:$ENV{removals})\b//g; s/^,//' "$1"
It reads the servers to remove into an array, joins that into a pipe-separated string, and then uses that in the perl regular expression to remove all the servers in a single pass through the file. Slashes and other funky characters (As long as they're not RE metacharacters) won't mess up the parsing of the perl, because it uses the environment variable instead of embedding the string directly. It also uses a word boundry so that removing server2 won't remove that part of server22.
I would like to add the text foo to the start of all files in a certain directory. I tried the following command:
sed '1i foo' *
But that only added the text to the first file. How can I append to all files in a single sed command? (I know that it can be done with a for loop, I'm specifically asking for a single sed command)
Use option --separate (or short: -s) to consider files as separate rather than as a single continuous long stream.
If you want to alter the files, just add the -i flag:
sed -i '1i foo' *
It'll add foo at the beginning of every file.
Note: without -i, the files weren't actually modified. foo was added at the beginning of the whole content to the standard output only, thus appearing only once.
How about:
sed -i '1 s/^/foo/g' *
I have a template file I want to copy and then edit from a script, inserting content at specific template points. For example, my template file might be something like,
...
rm -rf SomeDirectory
make install
#{INSERT-CONTENT-HERE}
do-something-else
...
In another script, I want to add content at "#{INSERT-CONTENT-HERE}" within a loop, i.e.
for i in c; do
# Write content to the template file copy at the correct point.
done
I think sed is the right tool, but I'm not familiar enough to know the syntax, and the man page isn't helping.
An example:
echo "Line #{INSERT-CONTENT-HERE}" | sed 's/#{INSERT-CONTENT-HERE}/---/'
To modify a file:
sed -i 's/#{INSERT-CONTENT-HERE}/---#{INSERT-CONTENT-HERE}/' filename
where -i means in-place edit so be warned
if you do:
sed -i.bak 's/#{INSERT-CONTENT-HERE}/---/' filename
it should back up original as filename.bak
also to make multiple substitutions at each line use the g flag:
sed -i.bak 's/#{INSERT-CONTENT-HERE}/---/g' filename
You can copy the output of all the commands into a temporary file and then copy the contents of that entire file into the template file:
TEMPFILE=`mktemp` && (
for i in c
echo "SomeTextBasedOn $i" >> $TEMPFILE
done
sed -i '/{INSERT-CONTENT-HERE}/r '$TEMPFILE targetfile
rm $TEMPFILE
)