I have a big text file URL.txt. I want to print every second line on the terminal (without altering the content of the file) after line number 40 using sed command.
With GNU sed you can do
sed -n '40~2 p' file
Related
I have a file with this content:
lines
lines
rootdev=UUID=967d8dc3-f595-4a6e-929e-cc89as5a1a2s / ext4 defaults,
lines
I am searching for one line command which should strip everything in the line rootdev after whitespace, so the final content should be like:
lines
lines
rootdev=UUID=967d8dc3-f595-4a6e-929e-cc89as5a1a2s
lines
Any idea how to do it with one line command? (so I do not need to open nano with this file and do it manually)
I tried with sed but it just replaces the word rootdev
sed -i 's/rootdev//g' file.txt
Your attempt with sed can't work because it would just remove rootdev string with an empty string. What you need is a tool that matches a pattern and does an action on that whole line for which I think awk is more recommended than sed.
Using awk to match the line to strip off the spaces using gsub() should be sufficient,
awk '/^rootdev/{ gsub(/[[:space:]].*/,"",$0) }1' file
If you are using GNU awk with version greater than 4.1.0, you could use its in-place edit option to make the changes dynamically
gawk -i inplace '/^rootdev/{ gsub(/[[:space:]].*/,"",$0) }1' file
for earlier versions, use a temporary file
awk '/^rootdev/{ gsub(/[[:space:]].*/,"",$0) }1' file > temp && mv temp file
or use sponge from moreutils. If its not available in your system do get it on RHEL using yum install moreutils or with apt-get in Debian.
awk '/^rootdev/{ gsub(/[[:space:]].*/,"",$0) }1' file | sponge file
First, search for a line beginning with rootdev=, and when you find it delete everything after the first whitespace until the end of line.
sed -i '/^rootdev=/ s/ .*$//' file
Using a capturing group to keep rootdev=... part in, and replacing the whole line with it is an option too.
sed -i 's/^\(rootdev=[^ ]*\).*$/\1/' file
I have a text file and I need a command using sed to insert a blank line after every line that that consists of capital letters and spaces only.
This might work for you (GNU sed):
sed '/^[[:blank:][:upper:]][[:blank:][:upper:]]*$/G' file
This appends the hold space (by default it contains a newline) to lines containing at least one or more whitespace or uppercase characters.
Given:
$ cat file
LINE LINE LINE
Line Line Line
Line 1
LINE 2
END!
====
You can use s/// to add a \n to the line:
With POSIX sed, use a literal new line in the sed script:
$ sed 's/^\([[:upper:][:blank:]]*\)$/\1\
/' file
LINE LINE LINE
Line Line Line
Line 1
LINE 2
END!
====
With GNU sed, you can use the representation of \n:
$ sed 's/^\([[:upper:][:blank:]]*\)$/\1\n/' file
You can also use a\ to append in sed. I have tried to get sed append to work but cannot reliably with POSIX, BSD and GNU sed since POSIX and BSD do not support \n
With GNU sed (note space after a\):
$ sed '/^[[:upper:][:blank:]]*$/a\ ' file
BSD:
$ sed '/^[[:upper:][:blank:]]*$/a\
\
' file
Those are not exactly equivalent since the GNU version has a space on the blank line.
The version of POSIX sed I have did not work with either of those...
Given the platform and version differences of sed, you might consider awk to do this since simple awk's are easier to make universal.
This works on every awk I have:
$ awk '1; /^[[:upper:][:blank:]]*$/{print ""}' file
With awk you can also make it so that blank lines are not doubled by making sure there is at least non blank like so:
$ awk '1; /^[[:upper:][:blank:]]+$/ && NF>1 {print ""}' file
Sure. Just insert lines with a:
sed '/^[[:blank:]A-Z]*$/a\'
The a command inserts the string after it after every matching line (end the string with a backslash). So the above command just inserts an empty line after all lines that contains solely of capital letters and spaces. That's exactly what you want.
I want to insert word after nth line after pattern using sed.
I tied to modify this command but it inserts only in first line after pattern.
sed -i '/myPattern/a \ LineIWantToinser ' myFile
What command should I use to insert for example in third line after pattern?
Easiest way to do it with GNU sed is.. (maybe some direct solution exists!?)
sed -n '/pattern/=' file
to see line where pattern is (grep also can be used here with -n)
then if linenumber+ numoflines is for example 123
sed '123aSOME INSERTED TEXT AFTER THAT LINE' file
where little a is append command (after that line, if i is used will be pre pattern line)
ps. I'm eager to see if #neronlevelu (or other sed Lover) will find some better sed solution.
Edit: i've found it, it seems a for append or i for insert must? be on first position on line when using { with ; inside } like
sed '/pattern/{N;N;N;
a SOME TEXT FOR INSERTING
}' file
sed '/pattern/{N;N;N;i \
Line to add after 3 lines with patterne as starting counter
' YourFile
number of N to add line between pattern and inserted line.
there is no check for end of file or pattern in the 3 lines. (not specified in PO)
A version with bash and ed:
ed -s myFile <<<$'/myPattern/+3a\n LineIWantToinser \n.\nwq'
ed enables us to use the line addressing /myPattern/+3.
Say I have some arbitrary multi-line text file:
sometext
moretext
lastline
How can I remove only the last character (the e, not the newline or null) of the file without making the text file invalid?
A simpler approach (outputs to stdout, doesn't update the input file):
sed '$ s/.$//' somefile
$ is a Sed address that matches the last input line only, thus causing the following function call (s/.$//) to be executed on the last line only.
s/.$// replaces the last character on the (in this case last) line with an empty string; i.e., effectively removes the last char. (before the newline) on the line.
. matches any character on the line, and following it with $ anchors the match to the end of the line; note how the use of $ in this regular expression is conceptually related, but technically distinct from the previous use of $ as a Sed address.
Example with stdin input (assumes Bash, Ksh, or Zsh):
$ sed '$ s/.$//' <<< $'line one\nline two'
line one
line tw
To update the input file too (do not use if the input file is a symlink):
sed -i '$ s/.$//' somefile
Note:
On macOS, you'd have to use -i '' instead of just -i; for an overview of the pitfalls associated with -i, see the bottom half of this answer.
If you need to process very large input files and/or performance / disk usage are a concern and you're using GNU utilities (Linux), see ImHere's helpful answer.
truncate
truncate -s-1 file
Removes one (-1) character from the end of the same file. Exactly as a >> will append to the same file.
The problem with this approach is that it doesn't retain a trailing newline if it existed.
The solution is:
if [ -n "$(tail -c1 file)" ] # if the file has not a trailing new line.
then
truncate -s-1 file # remove one char as the question request.
else
truncate -s-2 file # remove the last two characters
echo "" >> file # add the trailing new line back
fi
This works because tail takes the last byte (not char).
It takes almost no time even with big files.
Why not sed
The problem with a sed solution like sed '$ s/.$//' file is that it reads the whole file first (taking a long time with large files), then you need a temporary file (of the same size as the original):
sed '$ s/.$//' file > tempfile
rm file; mv tempfile file
And then move the tempfile to replace the file.
Here's another using ex, which I find not as cryptic as the sed solution:
printf '%s\n' '$' 's/.$//' wq | ex somefile
The $ goes to the last line, the s deletes the last character, and wq is the well known (to vi users) write+quit.
After a whole bunch of playing around with different strategies (and avoiding sed -i or perl), the best way i found to do this was with:
sed '$! { P; D; }; s/.$//' somefile
If the goal is to remove the last character in the last line, this awk should do:
awk '{a[NR]=$0} END {for (i=1;i<NR;i++) print a[i];sub(/.$/,"",a[NR]);print a[NR]}' file
sometext
moretext
lastlin
It store all data into an array, then print it out and change last line.
Just a remark: sed will temporarily remove the file.
So if you are tailing the file, you'll get a "No such file or directory" warning until you reissue the tail command.
EDITED ANSWER
I created a script and put your text inside on my Desktop. this test file is saved as "old_file.txt"
sometext
moretext
lastline
Afterwards I wrote a small script to take the old file and eliminate the last character in the last line
#!/bin/bash
no_of_new_line_characters=`wc '/root/Desktop/old_file.txt'|cut -d ' ' -f2`
let "no_of_lines=no_of_new_line_characters+1"
sed -n 1,"$no_of_new_line_characters"p '/root/Desktop/old_file.txt' > '/root/Desktop/my_new_file'
sed -n "$no_of_lines","$no_of_lines"p '/root/Desktop/old_file.txt'|sed 's/.$//g' >> '/root/Desktop/my_new_file'
opening the new_file I created, showed the output as follows:
sometext
moretext
lastlin
I apologize for my previous answer (wasn't reading carefully)
sed 's/.$//' filename | tee newFilename
This should do your job.
A couple perl solutions, for comparison/reference:
(echo 1a; echo 2b) | perl -e '$_=join("",<>); s/.$//; print'
(echo 1a; echo 2b) | perl -e 'while(<>){ if(eof) {s/.$//}; print }'
I find the first read-whole-file-into-memory approach can be generally quite useful (less so for this particular problem). You can now do regex's which span multiple lines, for example to combine every 3 lines of a certain format into 1 summary line.
For this problem, truncate would be faster and the sed version is shorter to type. Note that truncate requires a file to operate on, not a stream. Normally I find sed to lack the power of perl and I much prefer the extended-regex / perl-regex syntax. But this problem has a nice sed solution.
I can grap a specific line from a file using sed. Is there an easy way to take this line or paragraph and insert onto a specific line in another file?
sed -n 1,10p >> foo appends the result to foo, which places it at the bottom. Is there a standard unix tool to insert onto a specific line?
Perhaps you are looking for sed's r command?
sed '123r file.txt' main.txt
inserts the contents of file.txt at line 123 of main.txt, printing everything to standard output.
(If your sed has the -i option, you can make it modify main.txt directly; otherwise, it will not modify its input files.)
If you want to replace the nth line in file foo you can do it with
cp foo foo.tmp
head -n $((n-1)) foo.tmp > foo
echo "newline" >> foo
tail -n +$((n+1)) foo.tmp >> foo
So you take the first n-1 lines with head -n NR, append your new line and then append the rest starting from line n+1 with tail -n +NR.
This might work for you (GNU sed):
sed '123s|.*|sed '\''1,10!d'\'' insert.txt|e' main.txt