CODEWITHSUNDEEP
regexubuntusedmakefile
Athylus
Athylus

Reputation: 191

Sed on a Makefile

I want to replace my default make target using sed in a shellscript. First I am trying to get sed to work from command line.

My makefile contains:

all:
    gcc -Wall -o main main.c

I want it to contain:

all:
        gcc -Wall -o TEST main.c

The sed command I use:

sed -i 's/(-o[ ][^ ]+)/-o TEST/g' Makefile

It seems to work on https://regexr.com/ but when I run the command in ubuntu it does not edit my Makefile. What could be the reason?

Also is main the default make target, or is main.c the default make target? Some terminology things I don't quite understand yet.

Upvotes: 2

Views: 527

Answers (2)

tripleee
tripleee

Reputation: 189417

The proper soulution is to parametrize the Makefile.

MAIN := main
all:
    gcc -Wall -o $(MAIN) main.c

Now you can say make MAIN=TEST (or make MAIN=fnord or what have you) without modifying anything.

Modifying code is nearly always the wrong solution (whereas generating code can be a powerful and versatile technique).

Upvotes: 1

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626870

You are using the BRE (not ERE) POSIX flavor, so the unescaped ( and ) in your pattern match literal parentheses and + is also parsed as a literal plus symbol. To create a capturing group in a BRE POSIX pattern, you need to use escaped parentheses. Anyways, the parentheses are redundant in the current regex pattern since you are not using placeholders in the replacement pattern. In GNU sed, you may still use + in BRE patterns as a 1+ occurrences quantifier, but you need to escape it.

Use

sed -i 's/-o [^ ]\+/-o TEST/g' Makefile

Or

sed -i 's/-o [^ ][^ ]*/-o TEST/g' Makefile

to fix the issue. See the online demo.

Note that \+ quantifier is not recognized by all sed versions, thus, [^ ][^ ]* (a non-space followed with 0+ non-spaces) workaround might turn out useful.

Upvotes: 0

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