CODEWITHSUNDEEP
replacesed
user991269
user991269

Reputation: 1

SED help: how to substitute a string with another containing square brackets

I am using OSX and I'm having a problem while trying to replace a string in a file using the sed command. The problem is that the substitute string contains a square bracket. In particular I want to replace this string "message--------------" (- are blanks)
with this one "message------[ yea ]"

but if I type

sed "message              /s//message     \ [ yea ]" filein > fileout

I get this message: bad flag in substitute command: '['

I tried to put a \ before the [ but it didn't work. Can anyone help? Thanks!

Upvotes: 0

Views: 4099

Answers (2)

Michael J. Barber
Michael J. Barber

Reputation: 25032

Try this:

sed 's/message    /&[ yea ]/g' filein > fileout

The & is the expression matched. No special treatment is needed for the brackets.

It wasn't really clear to me how the spaces were intended to be handled. The above just adds [ yea ] to the end of the fixed-length sequence of spaces. Should it be preferred to replace the last spaces of an arbitrary-length sequence of spaces with [ yea ], a more complicated command is needed: 

sed 's/\(message \{1,\}\)       /\1[ yea ]/g' filein > fileout

The idea in this case is to match a pattern that has two parts. First is a group, bracketed by \( \), which looks for the message followed by one or more spaces (\{1,\}. This must be followed by exactly seven spaces. When matching text is found, it is replaced by the text of the group (the \1, indicating the first group) followed by [ yea ]. The strategy here can be adapted to other search-replace patterns, with, e.g., multiple groups or different text.

Upvotes: 1

user unknown
user unknown

Reputation: 36229

Without counting the blanks exactly:

echo "message         foo" | sed "s/message        /message [ yea ]/"

message [ yea ] foo

The substitute-command is 's/IN/OUT/', while 'm...' is unknown - no m-command known. Another key to success, is, to mask the single character [ immediately, without a blank in between, with a backslash. However - on the right side of a substitution-expression, a group does not make much sense, so you don't need to mask them.

Upvotes: 0

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