Example Grep's and Awk's Update 1

#!/bin/bash

# defines
cat /usr/include/sys/stat.h | grep "#define "
# conditional defines
cat /usr/include/sys/stat.h | grep "# define "

# all root ifdefs
cat /usr/include/sys/stat.h | awk '/# ifdef/,/# endif/'1
# all code inbetween ifdef
cat /usr/include/sys/stat.h | awk '/# ifdef/,/# endif/'$1
cat /usr/include/sys/stat.h | awk '/# ifdef/,/# endif/'

# define tree
cat /usr/include/sys/stat.h | awk '/#[ ]{0,}define/'

# ifdef, define, endif tree
grep -E "(#[ ]{0,}define|#[ ]{0,}ifdef|#[ ]{0,}endif)" /usr/include/sys/stat.h

# list all includes
grep -iE "#[ ]{0,}include" /usr/include/sys/stat.h

# list all error codes in a c header file ( -P used to detect tabs )
grep -P "^#define( |\t){1,}E.*[0-9]{1,3}" /usr/include/asm-generic/errno.h

# list all error codes in all c header files in /usr/include folder and it's subfolders
for e in `slocate "/usr/include/*.h"`; do grep -P "^#define( |\t){1,}E.*[0-9]{1,3}" $e; done

# list include tree
grep -iE "#[ ]{0,}include" /usr/include/sys/stat.h

# list full file (*not finished)
grep -E "(#[ ]{0,}define|#[ ]{0,}ifdef|#[ ]{0,}endif|#[ ]{0,}include)" /usr/include/sys/stat.h

# ifdef, define, endif, include tree
grep -E "#[ ]{0,}(define|ifdef|ifndef|endif|include)" /usr/include/sys/stat.h

grep -iE "^[ ]{0,}[struct]{6}[ ]{1}.*" /usr/include/bits/statx.h
grep -iE "(#[ ]{0,}(define|ifndef|ifdef|endif|include|error)|^[ ]{0,}struct )" /usr/include/bits/statx.h

# extract text from .msg format, could be improved
cat Draft\ email\ cover\ letter.msg | grep -Eao "[A-Za-z0-9 \.\(\)\\\/\-]" | tr -d '\n' > ~/draft-extract

# find inode/(folders/subfolders) usage in folders
find / -xdev -printf '%h\n' | sort | uniq -c | sort -k 1 -n > ~/inode-usage.folders-`date +%j.%Y` # find inode usage in folders
du --inodes -xS / > ~/inode-usage\(du\).folders-`date +%j.%Y` # find inode usage in folders

# replace octal terminal escape coded colours with conky colours
sed 's/\(\\\033\[3\)\(.\)\(m\)/{color fg \2}/g' # foreground color ( replace 0-7 with conky colour names )
sed 's/\(\\\033\[4\)\(.\)\(m\)/{color bg \2}/g' # background color ( replace 0-7 with conky colour names )

#Extract xml tag from line
grep -iE "<title>.*</title>"

# Make more generic ( removes need for loops in a lot of situations in bash scripts )
SKIP=`cat Regions | head -n4 | sed -e s/"\n"/"|"/g`; # region file contains lists of citys to group into regions comma separated for citys, endline for regions ( from xero-grab.sh )
cat $NAME | grep -iE "<(City|Region)>" | grep -i "$l" | grep -viE "($(exec echo $SKIP))" > /dev/null; # grep skip with | or for citys for a single region

# Find variables in a Makefile
function get-vars-from-makefile()
{
    IFS=$',';
    for i in `cat Makefile | \
            grep "CC" | \
            grep -Eo "\\$\\([A-Z]{1,}\\)" | \
            sort | \
            uniq | \
            cut -c3- | rev | cut -c2- | rev | \
            tr '\n' ',' | \
            rev | cut -c2- | rev`;
    do
        echo "$i";
    done
}
# match a regex and for a c header, and insert comment to front ( & symbol in sed regex used to re-print whole match ($_ for whole line) )
cat somefile.cpp | sed -E s/"^[ ]{0,}#include.*boost"/"\\/\\/&"/