Delete all lines before first occurrence of specific string in file

Question

Basically I have a file like:

junk
morejunk
somestring
bats
car
somestring
bats
car
somestring
bats
car

and I want to remove all of the junk before the first occurrence of somestring so the file looks like

somestring
bats
car
somestring
bats
car
somestring
bats
car

I followed the advice from this question to use sed -i '0,/somestring/,d' file.txt but it deletes the line with the first occurrence of somestring, when I want to keep that line as the first line.

score 21 · Accepted Answer · answered Mar 13 '16 at 03:14

21

With sed you could use:

sed -i '/somestring/,$!d' file

Explanation of replace expressions:

_{, matches lines starting from where the first
address matches, and continues until the second match
(inclusively).}

_{$ matches the last line of the last file of input,
or the last line of each file when the -i or -s options are
specified.}

_{! If the character follows an address range, then only lines
which do not match the address range will be selected.}

_{d Delete the pattern space; immediately start next cycle.}

Result:

$ sed -i '/somestring/,$!d' file
somestring
bats
car
somestring
bats
car
somestring
bats
car

answered Mar 13 '16 at 03:14

l'L'l

44,951
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1

Thank you. (years later...) This helped me a lot. – Ryan Porter May 28 '21 at 18:06
1

For those who want to after a match it would be something like this: `sed '/-----END CERTIFICATE-----/q;$d'` – doublespaces Aug 26 '21 at 22:47

score 3 · Answer 2 · answered Mar 13 '16 at 02:45

Here's a way you can do it using awk:

awk '/somestring/ { f = 1 } f' file

When the pattern matches, set f to true. When f becomes true, print each line.

Another option, slightly more cryptic:

awk 'f += /somestring/' file

f is increased by either 1 when the pattern matches or 0 when it doesn't. Once a line has matched the pattern, the expression becomes true, so each line is printed.

score 3 · Answer 3 · answered Mar 13 '16 at 03:09

3

$ sed -n '/somestring/,$p' infile
somestring
bats
car
somestring
bats
car
somestring
bats
car

The command suppresses printing with -n, and then for the address range /somestring/,$, i.e., from somestring to the last line, executes the p command to print the line.

answered Mar 13 '16 at 03:09

Benjamin W.

46,058
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I offered a [different solution](http://stackoverflow.com/a/35965998/1301972) based on code the OP already had at hand, but yours is a better sed-only solution. Your solution also works with both GNU and BSD seds, so +1 for that. – Todd A. Jacobs Mar 13 '16 at 03:12
@CodeGnome Appreciate it! – Benjamin W. Mar 13 '16 at 03:13

score 2 · Answer 4 · answered Mar 13 '16 at 03:22

2

another idiomatic awk solution (and fewest keystrokes) is

$ awk '/somestring/,0' file   

somestring
bats
car
somestring
bats
car
somestring
bats
car

answered Mar 13 '16 at 03:22

karakfa

66,216
7
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score 0 · Answer 5 · answered Mar 13 '16 at 03:10

Concatenate with Echo and GNU Sed

You had most of the solution with GNU sed, which allows you to use both line numbers and regular expressions in range patterns. All you really need to do to get the behavior you want is to prepend the string you're using as your end-pattern to the resulting output.

For example:

$ str='somestring'; echo -e "${str}\n$(sed "0,/${str}/d" /tmp/corpus)"
somestring
bats
car
somestring
bats
car
somestring
bats
car

Basically, you assign the pattern to str, which you then reuse in both the echo statement and the sed expression. If you run into quoting problems related to variable interpolation, just replace the str variable with fixed strings in both your echo and sed commands. However, works as-is with the posted corpus.

Delete all lines before first occurrence of specific string in file

5 Answers5

Concatenate with Echo and GNU Sed

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