The tcpdump arguments are just an example.
Using sed to extract lines in a text file
If you write bash scripts a lot, you are bound to run into a situation where you want to extract some lines from a file. Yesterday, I needed to extract the first line of a file, say named somefile.txt.
cat somefile.txt
Line 1
Line 2
Line 3
Line 4
This specific task can be easily done with this:
head -1 somefile.txt
Line 1
For a more complicated task, like extract the second to third lines of a file. head is inadequate.
So, let's try extracting lines using sed: the stream editor.
My first attempt uses the p sed command (for print):
sed 1p somefile.txt
Line 1
Line 1
Line 2
Line 3
Line 4
Note that it prints the whole file, with the first line printed twice. Why? The default output behavior is to print every line of the input file stream.
The explicit 1p command just tells it to print the first line .... again.
To fix it, you need to suppress the default output (using -n), making explicit prints the only way to print to default output.
sed -n 1p somefile.txt
Line 1
Alternatively, you can tell sed to delete all but the first line.
sed '1!d' somefile.txt
Line 1
'1!d' means if a line is not(!) the first line, delete.
Note that the single quotes are necessary. Otherwise, the !d will bring back the last command you executed that starts with the letter d.
To extract a range of lines, say lines 2 to 4, you can execute either of the following:
sed -n 2,4p somefile.txt
sed '2,4!d' somefile.txt
Note that the comma specifies a range (from the line before the comma to the line after).
What if the lines you want to extract are not in sequence, say lines 1 to 2, and line 4?
sed -n -e 1,2p -e 4p somefile.txt
Line 1
Line 2
Line 4
Show Sample Output
If your version of curl does not support the --compressed option, use
curl -s http://funnyjunk.com | gunzip
instead of
curl -s --compressed http://funnyjunk.com
nothing special Show Sample Output
Use matched data and some other as replacement data Show Sample Output
Can't print correctly in the command field.
There is a new line before } as follows
seq 20 | sed -n '5,6 { w out.txt
}'
Show Sample Output
In case sed and awk are not available you may use this to remove the last character from a string with "rev" and "cut". Show Sample Output
Helps if you accidentally deleted files from an svn repo with plain rm and you would like to mark them for svn to delete too.
Uses sed with a regex to move the linenumbers to the line end. The plain regex (w/o escapes) looks like that: ^([^:]*):(.*) Show Sample Output
sed '4~5,+1d' file.txt 1 2 3 6 7 8 Show Sample Output
Just an other solution :)
Remove ANSI colors from stream or file
reverse of my previous command 10006 Show Sample Output
It remove the square bracket and convert UNIX time to human readable time for all line of a stream (or file). Show Sample Output
Not figured by me, but a colleague of mine. See the total amount of data on an AIX machine. Show Sample Output
Delete range of lines. Ex: Line 6 through 66 in .
Simpler and without all of the coloring gimmicks. This just returns a list of branches with the most recent first. This should be useful for cleaning your remotes. Show Sample Output
This was done in csh. Show Sample Output
Shows sorted by query time, the headers of mysqlbinlog entries. Then is easy to locate the heavier events on the raw log dump Show Sample Output
Show the crontabs of all the users. Show Sample Output
This probably only works without modifications in RHEL/CentOS/Fedora. Show Sample Output
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