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Suppose using the pkg-config I can find which link flags are needed add a library to my code, suppose if I need cairo libraries to add, I can find the appropriate -l flag by 

> pkg-config --libs cairo
> -lcairo

How do I find the reverse (i.e. link flags --> library name)? Suppose I want to know which library will be added by invoking -lm flag, how do I do that?

ramgorur
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1 Answers1

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Suppose I want to know which library will be added by invoking -lm flag, how do I do that?

The part after the -l is the name of the library. Its binary is prefixed with lib, so you can find them by that name;

> whereis libm
libm: /usr/lib64/libm.a /usr/lib64/libm.so

> whereis libcairo
libcairo: /usr/lib64/libcairo.so

Etc.

If whereis does not say anything, you can also try grepping the output of ldconfig -p (see man ldconfig):

> ldconfig -p | grep "libm.so"
    libm.so.6 (libc6,x86-64, OS ABI: Linux 2.6.32) => /lib64/libm.so.6
    libm.so.6 (libc6, OS ABI: Linux 2.6.32) => /lib/libm.so.6
    libm.so (libc6,x86-64, OS ABI: Linux 2.6.32) => /lib64/libm.so

Notice in this case I've appended "libm" with ".so", which is not necessary, but it saves matching against "libmfoo...", "libmbar...", etc. Since -l refers to linking shared object (.so) libraries, this should be pretty foolproof.

goldilocks
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  • thanks for the pointer, in my machine the `whereis` command does not give anything. Anyway I am managing it with the `locate` command for the time being. – ramgorur Mar 31 '14 at 22:18
  • Yes, `whereis` is not really intended for finding (shared) libraries, although it generally does work and the usage and output are simple. For cases where it doesn't I've added a paragraph above about grepping `ldconfig -p` instead. – goldilocks Apr 01 '14 at 03:09
  • If you don't know whether the library is installed, `apt-file search` is better. – Faheem Mitha Apr 01 '14 at 08:21