This question already has answers here:
Find and replace in file and overwrite file doesn't work, it empties the file
(12 answers)
sed edit file in place
(15 answers)
Closed 6 years ago.
I need to insert a command "new file" in a test.txt file at line number 4.
Tried sed; I can see the changed file output, but when I again do cat test.txt, the changes are gone.
sed "4i new file" /test.txt
How can I save the changes?
Use in place edit option sed -i "4i new file" test.txt
Without the -i option sed will not make any changes to the file. It will only print the result.
-i[SUFFIX], --in-place[=SUFFIX]
edit files in place (makes backup if SUFFIX supplied)
sed '4i new file' test.txt > tmp && mv tmp test.txt
Related
This question already has answers here:
How to replace a string in multiple files in linux command line
(28 answers)
How can I use a file in a command and redirect output to the same file without truncating it?
(14 answers)
Looping through the content of a file in Bash
(16 answers)
How to loop over files in directory and change path and add suffix to filename
(6 answers)
Closed 3 years ago.
I have numerous files in a directory and want to replace one of the libraries used in all of these files with a newer library because the old library no longer works.
I have used ls > names.txt to list all filenames into a txt document. I then attempted to write a bash script which would loop through all files, catch the old library, and replace it with the new library.
for entry in names.txt
do
sed 's/<libOld>/<libNew>/g' $entry > $entry
done
I expect the loop to go through each file name, find the old library used, and replace it with the new one. Running this script however doesn't appear to do anything.
You're bumping into a few common issues; I've closed as a duplicate, but here are the collected fixes for your specific case:
Editing a file in-place with sed
With GNU sed:
sed -i 's/<libOld>/<libNew>/g' filename
with any sed:
sed 's/<libOld>/<libNew>/g' filename > filename.tmp && mv filename.tmp filename
Looping over a file line by line
for entry in names.txt only ever sets entry to names.txt, it doesn't read its contents. This is also BashFAQ/001.
while IFS= read -r entry; do
printf '%s\n' "$entry"
done < names.txt
Looping over all files in a directory
You don't need a separate file, and you shouldn't use ls but globs:
for fname in ./*; do
printf '%s\n' "$fname"
done
Combined for your case
Notice the double quotes around $entry.
for entry in ./*; do
sed -i 's/<libOld>/<libNew>/g' "$entry"
done
which can be simplified to no loop at all:
sed -i 's/<libOld>/<libNew>/g' ./*
This question already has answers here:
Extract filename and extension in Bash
(38 answers)
Closed 6 years ago.
So I have put a load of names of files in a text file, these are specifically .log files:
ls *.log > finished_data.txt
Now that I Have the list of .log files, how do I keep the names but remove the .log extension?
My thought process is renaming them all?
Just loop through the .log files and move them:
for file in *.log
do
mv "$file" "${file%.log}"
done
This uses shell parameter expansion:
$ d="a.log.log"
$ echo "${d%.log}"
a.log
Using rename to rename all .log files by removing .log from the end:
rename 's/\.log$//' *.log
\.log$ matches .log at the end of the file name and it is being omitted by replacing with blank
If you are using prename, then you can do a dry-run first:
rename -n 's/\.log$//' *.log
If satisfied with the changes to be made:
rename 's/\.log$//' *.log
This question already has answers here:
sed edit file in place
(15 answers)
Closed 8 years ago.
I need a script that add a particular character to the end of each line . I am using the command
sed 's/$/ foo/' r.txt
It adds foo to end of each line in the file r.txt and displays in my terminal .
What do i need to do if i want to save this existing file with this new record appended after the end of each line .
To save to a new file:
sed 's/$/ foo/' r.txt > newfile.txt
To edit in place
sed -i 's/$/ foo/' r.txt
This question already has answers here:
Appending a line to a file only if it does not already exist
(25 answers)
Closed 1 year ago.
I want to add the following line:
nohup java -jar /mnt/fusion/nfs/labStats/LabInfoAutoLog.jar > /dev/null &
to the end of the file /etc/rc.d/rc.local if it does not already exist.
How can I do that from linux command line? I assume grep or sed would work, but I am not familiar enough with either to get it to work. Right now I use echo, but that just keeps adding it over and over again.
Assuming you want it at the end of the file:
LINE="nohup java -jar /mnt/fusion/nfs/labStats/LabInfoAutoLog.jar > /dev/null &"
FILE=/etc/rc.d/rc.local
grep -q "$LINE" "$FILE" || echo "$LINE" >> "$FILE"
one option is two steps:
grep -q "yourline" /path/file||sed -i '/..place../ a \the line' file
also possible to do with awk,
save all lines in array, during saving if the line was found, exit. otherwise, add the line in END{} block to the right place.
P.S. You didn't tell in the file, where to add that line.
I was doing some hands-on with the Unix sed command. I was trying out the substitution and append command, in a file. But the difficulty is, I have to create an intermediate file, and then do mv to rename it to the original file.
Is there any way to do it at one shot in the same file?
[root#dhcppc0 practice]# sed '1i\
> Today is Sunday
> ' file1 > file1
[root#dhcppc0 practice]# cat file1
[root#dhcppc0 practice]#
The file is deleted!
[root#dhcppc0 practice]# sed 's/director/painter/' file1 > file1
[root#dhcppc0 practice]# cat file1
The file is deleted!
Try this -
sed -i '' 's/originaltext/replacementtext/g' filename | cat filename
-i '' is meant for providing a backup file. If you are confident your replacement won't cause an issue you can put '' to pass no backup file
/g is for replacing globally. If you have more than one originaltext in one line then with /g option will replace all else it will only replace the first.
GNU sed knows an option -i which does in-place edit of the given files.
When doing an operation file1 > file1 what actually happens is, that the file is opened and truncated by the shell before the program (which gets it's name as argument) comes around reading anything from it.
Update:
sed's man page states the following on the -i option (thanks Delan for mentioning it):
-i[SUFFIX], --in-place[=SUFFIX]
edit files in place (makes backup if extension supplied)
sed -i.bak 's/director/painter/' file1
-i[SUFFIX], --in-place[=SUFFIX]
edit files in place (makes backup if extension supplied)