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6.41. Flex-2.5.35

The Flex package contains a utility for generating programs that recognize patterns in text.

Approximate build time: 0.7 SBU
Required disk space: 28 MB

6.41.1. Installation of Flex

Apply a patch that fixes a bug in the C++ scanner generator, that causes scanner compilation to fail when using GCC-4.5.1:

patch -Np1 -i ../flex-2.5.35-gcc44-1.patch

Prepare Flex for compilation:

./configure --prefix=/usr

Compile the package:


To test the results (about 0.5 SBU), issue:

make check

Install the package:

make install

There are some packages that expect to find the lex library in /usr/lib. Create a symlink to account for this:

ln -sv libfl.a /usr/lib/libl.a

A few programs do not know about flex yet and try to run its predecessor, lex. To support those programs, create a wrapper script named lex that calls flex in lex emulation mode:

cat > /usr/bin/lex << "EOF"
# Begin /usr/bin/lex

exec /usr/bin/flex -l "$@"

# End /usr/bin/lex
chmod -v 755 /usr/bin/lex

If desired, install the flex.pdf documentation file:

mkdir -v /usr/share/doc/flex-2.5.35
cp    -v doc/flex.pdf \

6.41.2. Contents of Flex

Installed programs: flex and lex
Installed libraries: libfl.a and libfl_pic.a

Short Descriptions


A tool for generating programs that recognize patterns in text; it allows for the versatility to specify the rules for pattern-finding, eradicating the need to develop a specialized program


A script that runs flex in lex emulation mode


The flex library