Remove The Lines Starting with a Character in Shell

Delete all lines beginning with a # from a file

This can be done with a sed one-liner:

sed '/^#/d'

This says, "find all lines that start with # and delete them, leaving everything else."

Remove the lines starting with a character in shell

Use grep with -E option for regex (or egrep in short):

grep -E "^[0-9].*" file.txt

Bash - remove all lines beginning with 'P'

Explanation

1. use ^ to anchor your pattern to the beginning of the line ;
2. delete lines matching the pattern using sed and the d flag.

Solution #1

cat file.txt | sed '/^P/d'

Better solution

Use sed-only:

sed '/^P/d' file.txt > new.txt

How to delete newline and character at the start of line using Bash?

With Perl.

perl -i -0777pe 's/\n"""/"/' new.txt

Output to new.txt:

"AAA"AAA
"BBB"BBB
"CCC"CCC

How to delete from a text file, all lines that contain a specific string?

To remove the line and print the output to standard out:

sed '/pattern to match/d' ./infile

To directly modify the file – does not work with BSD sed:

sed -i '/pattern to match/d' ./infile

Same, but for BSD sed (Mac OS X and FreeBSD) – does not work with GNU sed:

sed -i '' '/pattern to match/d' ./infile

To directly modify the file (and create a backup) – works with BSD and GNU sed:

sed -i.bak '/pattern to match/d' ./infile

How do you delete all lines that begin with string in unix sh?

grep -v '^string' yourfile.txt > stripped.txt

Remove the lines starting with a character in shell, but preserve the negative values

You can try like this:

grep '^ *[-+]\?[0-9]\+' file.txt > out.txt

(Or)

grep -E '^ *[-+]?[0-9]+' file.txt > out.txt

How can i remove a line only if it is followed by a line that starts with the same character?

If the whole file follows that pattern (some number of lines starting with >, of which you want only the last, followed by a single line that should always be printed), you could use something like this:

awk '/^>/ { latest=$0 } !/^>/ { if (latest) { print latest; latest="" } print }'

If the line starts with >, then it is remembered (stored in the variable latest) but not printed. If the line doesn't start with >, then it is printed, but only after first printing whatever was most recently stored in latest.

The conditional means each printed > line will appear only once, even if there are multiple non-> lines in a row. Since that doesn't happen in your sample data, you may not need the complication, and could use this simpler unconditional version:

awk '/^>/ { latest=$0 } !/^>/ { print latest; print }'

remove newline character after line starting with pattern

You can use the ORS output record sparator to do that very easily as

awk '$1 !~ /PATTERN/{ORS="\n"} $1 ~ /PATTERN/{ORS=" "} 1'

Example

$ awk '$1 !~ /PATTERN/{ORS="\n"} $1 ~ /PATTERN/{ORS=" "} 1' input
One
PATTERN bla bla bla Three
Four

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Or more simply like,

awk 'ORS = $1 ~ /PATTERN/ ? " " : "\n"'

Example

$ awk 'ORS = $1 ~ /PATTERN/ ? " " : "\n"' input
One
PATTERN bla bla bla Three
Four

What it does?

• ORS = $1 ~ /PATTERN/ ? " " : "\n" Sets the ORS to space or newline depending on the pattern match.

  Now expression always evaluates to true, in which case awk will print the entire input record.

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