How to insert a text at the beginning of a file?
It’s similar but I don’t want to create any new line with it. I would like to do this with sed if possible.
19 Answers 19
sed can operate on an address:
What is this magical 1s you see on every answer here? Line addressing!.
Want to add on the first 10 lines?
$ < echo -n ''; cat file; > >file.new $ mv file
-i stands for in-place, you can append a suffix to -i to make a copy rather than overwrite. -i.new would make a new file ending with .new, but just -i would edit the file directly.
Note that the sed won’t work on an empty file — afaict sed can’t be made to do anything at all with 0-length input.
If you want to add a line at the beginning of a file, you need to add \n at the end of the string in the best solution above.
The best solution will add the string, but with the string, it will not add a line at the end of a file.
On Mac OS, was getting error with «undefined label». Found that you need to give an extension for a backup file; see mkyong.com/mac/…
Under Mac OS’s sed version you have to supply backup file name with -i option. One can pass just an empty string for no backup like sed -i » ‘1s/^/new test\n/’ filename
If the file is only one line, you can use:
sed 's/^/insert this /' oldfile > newfile If it’s more than one line. one of:
sed '1s/^/insert this /' oldfile > newfile sed '1,1s/^/insert this /' oldfile > newfile I’ve included the latter so that you know how to do ranges of lines. Both of these «replace» the start line marker on their affected lines with the text you want to insert. You can also (assuming your sed is modern enough) use:
sed -i 'whatever command you choose' filename echo "$(echo -n 'hello'; cat filename)" > filename Unfortunately, command substitution will remove newlines at the end of file. So as to keep them one can use:
echo -n "hello" | cat - filename > /tmp/filename.tmp mv /tmp/filename.tmp filename Neither grouping nor command substitution is needed.
This is the superior and simpler solution to all the other ones using sed , which don’t work for empty files.
printf '%s' "some text at the beginning" | cat - filename This would only output the text followed by the file’s content, but it does not modify the file at all.
That’s a good solution, I wonder why it didn’t get any upvotes. Here’s mine my good sir. Also, why printf and not a simple echo ?
I tried directing this into a file by appending > file to the command, it jus spammed my terminal with «some text at the beginning»
sed -i '1i /path/of/file.sh' filename This will work even is the string containing forward slash «/»
To add a line to the top of the file:
Note that on OS X, sed -i file , fails. However, if you provide a backup extension, sed -i old file , then file is modified in place while file.old is created. You can then delete file.old in your script.
I’ve found macOS sed wants a dot to edit in place without creating a backup: sed -i.
echo "your header" > headerFile.txt cat yourFile >> headerFile.txt PROBLEM: tag a file, at the top of the file, with the base name of the parent directory.
/mnt/Vancouver/Programming/file1 tag the top of file1 with Programming .
SOLUTION 1 — non-empty files:
bn=$ ## bn: basename sed -i '1s/^/'"$bn"'\n/'
1s places the text at line 1 of the file.
SOLUTION 2 — empty or non-empty files:
printf "$\n" | cat - > temp && mv -f temp
Note that the — in the cat command is required (reads standard input: see man cat for more information). Here, I believe, it’s needed to take the output of the printf statement (to STDIN), and cat that and the file to temp . See also the explanation at the bottom of http://www.linfo.org/cat.html.
I also added -f to the mv command, to avoid being asked for confirmations when overwriting files.
To recurse over a directory:
for file in *; do printf "$\n" | cat - $file > temp && mv -f temp $file; done Note also that this will break over paths with spaces; there are solutions, elsewhere (e.g. file globbing, or find . -type f . -type solutions) for those.
ADDENDUM: Re: my last comment, this script will allow you to recurse over directories with spaces in the paths:
#!/bin/bash ## https://stackoverflow.com/questions/4638874/how-to-loop-through-a-directory-recursively-to-delete-files-with-certain-extensi ## To allow spaces in filenames, ## at the top of the script include: IFS=$'\n'; set -f ## at the end of the script include: unset IFS; set +f IFS=$'\n'; set -f # ---------------------------------------------------------------------------- # SET PATHS: IN="/mnt/Vancouver/Programming/data/claws-test/corpus test/" # https://superuser.com/questions/716001/how-can-i-get-files-with-numeric-names-using-ls-command # FILES=$(find $IN -type f -regex ".*/7*") ## recursive; numeric filenames only FILES=$(find $IN -type f -regex ".*/[0-9 ]*") ## recursive; numeric filenames only (may include spaces) # echo '$FILES:' ## single-quoted, (literally) prints: $FILES: # echo "$FILES" ## double-quoted, prints path/, filename (one per line) # ---------------------------------------------------------------------------- # MAIN LOOP: for f in $FILES do # Tag top of file with basename of current dir: printf "[top] Tag: $\n\n" | cat - $f > temp && mv -f temp $f # Tag bottom of file with basename of current dir: printf "\n[bottom] Tag: $\n" >> $f done unset IFS; set +f Command to append line to a text file without opening an editor
You can append a line of text to a file by using the >> operator:
echo "hello world" >> my_file.txt echo "alias list='ls -cl --group-directories-first'" >> config.fish I use echo myself, but be careful, if you only specify one > then the file will truncate, not append. for a safer command you can use sed: sed -i ‘$a hello world’ filename
explanation: -i will update the file (otherwise it will just print the result to stdout), $ is regex that will match the end of the file, and a appends the following text to filename.
echo «hello world» >> my_file.txt does not create a new last line with HW , but add it to the string of the last line.
Maybe «Hello World» @7wp 🙂 It’s echo that adds the line break (making it a line as opposed to just a bunch of characters). You can switch off the line break at the end with -n .
Adding to Stefano’s answer, you can also use cat :
$ cat >> config.fish alias list='ls -cl --group-directories-first' > EOF I often use this method but recently got caught when I pasted in a text that included some (escape) codes. It didn’t complain but when I checked the file there were chunks of pasted text missing. So use it with care!
@elmclose Sorry, which method? They work differently with respect to metacharacters. I think the second one doesn’t do anything with them, though there might be a few exceptions.
I meant EOF method. Very convenient and useful when you type or paste in readable text. But codes in my text confused the process. The file was a bash script that kept failing. Took me a while before I discovered what had happened.
There’s plenty of methods of appending to file without opening text editors, particularly via multiple available text processing utilities in Ubuntu. In general, anything that allows us to perform open() syscall with O_APPEND flag added, can be used to append to a file.
- GNU version of dd utility can append data to file with conv=notrunc oflag=append
printf "\nalias list='ls -cl --group-directories-first'\n" | dd conv=notrunc oflag=append bs=1 of=config.fish sed -i '$a alias list='"'"'ls -cl --group-directories-first'"'" config.fish #!/usr/bin/env python3 # read bytes from stdin, append to specified file import sys with open(sys.argv[1],'ab') as f: f.write(sys.stdin.buffer.read()) See also:
How to append multiple lines to a file
I am writing a bash script to look for a file if it doesn’t exist then create it and append this to it:
Host localhost ForwardAgent yes 10 Answers 10
# possibility 1: echo "line 1" >> greetings.txt echo "line 2" >> greetings.txt # possibility 2: echo "line 1 line 2" >> greetings.txt # possibility 3: cat > greetings.txt line 1 line 2 EOT # possibility 4 (more about input than output): arr=( 'line 1' 'line 2' ); printf '%s\n' "$" >> greetings.txt If sudo (other user privileges) is needed to write to the file, use this:
# possibility 1: echo "line 1" | sudo tee -a greetings.txt > /dev/null # possibility 3: sudo tee -a greetings.txt > /dev/null @ott-- You don't need a real subshell (i.e. can save one new process), this is enough: < echo "line 1" ; echo "line 2"; >>>greetings.txt
echo -e "Hello \nWorld \n" >> greetings.txt printf '%s\n %s\n' 'Host localhost' 'ForwardAgent yes' >> file.txt Or, if it's a literal tab that you want (rather than the four spaces in your question):
printf '%s\n\t%s\n' 'Host localhost' 'ForwardAgent yes' >> file.txt You can achieve the same effect with echo , but exactly how varies from implementation to implementation, whereas printf is consistent.
Another approach is to use tee
A few choice lines from tee 's man page:
The tee utility copies standard input to standard output, making a copy in zero or more files.
-a - Append the output to the files rather than overwriting them.
+1 tee tends to work with paths that require sudo (solutions that use > >> <
Here is an example to append multiple lines in a file:
< echo ' directory "/var/cache/bind";' echo ' listen-on < 127.0.0.1; >;' echo ' listen-on-v6 < none; >;' echo ' version "";' echo ' auth-nxdomain no;' echo ' forward only;' echo ' forwarders < 8.8.8.8; 8.8.4.4; >;' echo ' dnssec-enable no;' echo ' dnssec-validation no;' > >> your_file.txt It is worth to note that this variant is part of the ShellCheck recommendation github.com/koalaman/shellcheck/wiki/SC2129
SED can append a line to the end of a file like so:
sed -i '$ a text to be inserted' fileName.file
$ selects end of file, the a tells it to append, and after this comes the text that is to be inserted. Then of course the file name.
Does this approach have any added benefit than other solutions?
Yes, this approach has the added benefit of appending to any files return in a search, such as this: find . -name "*.html" -exec sed -i '$ a