Shell Programming and Scripting

# cat file
hello
flags this line starts with flags
world
#
# perl -i.bak -pe 's/^flags.*/new line/' file
#
# cat file
hello
new line
world
#

echo '2c
new line
.
w
q' | ex your_file

z=`sed '...' your_file`
echo "$z" >your_file

% mag show moreutils
moreutils is a growing collection of the unix tools that nobody thought to
write thirty years ago.

So far, it includes the following utilities:

 - sponge: soak up standard input and write to a file
 - ifne: run a program if the standard input is not empty
 - vidir: edit a directory in your text editor
 - vipe: insert a text editor into a pipe
 - ts: timestamp standard input
 - combine: combine the lines in two files using boolean operations
 - pee: tee standard input to pipes
 - zrun: automatically uncompress arguments to command
 - mispipe: pipe two commands, returning the exit status of the first
 - isutf8: check if a file or standard input is utf-8
 - lckdo: execute a program with a lock held
 - parallel: run multiple jobs at once

The 'ifdata' utility is not included in this FreeBSD port.

# ex equivalent of sed -i '/flags/s/.*/new $text/' file
ex -s file <<-"EOF"
        /^flags/s/.*/new $text/
        w
        q
EOF

# ex equivalent of sed -i.bak '/flags/s/.*/new $text/' file
ex -s file <<-"EOF"
        w %.bak
        /^flags/s/.*/new $text/
        w
        q
EOF

text=something
# ex equivalent of sed -i.bak "/flags/s/.*/new $text/" file
ex -s file <<-EOF
        w %.bak
        /^flags/s/.*/new $text/
        w
        q
EOF