ls, vim, sort, cat, sed cat, & awk

# delete all line in vim
:1,$d # starting at line 1, until the end of the line, delete.
# Strip HTML tags
sed -e 's/<[^>]*>//g'
# grep with or without "tab character"
|grep  -P "\t"
# sed, why
s/\(<td>\).*\(<\/td>\)/<td>TEXT_TO_REPLACE_BY<\/td>/g

# Unless boom is found replace aaa with bb# sed remove html tags
 '/boom/!s/aaa/bb/' file.txt

curl www.gnu.org | sed 's/<\/*[^>]*>//g'

# something...
cat > /tmp/h/a <<EOF

cassandra   soft   nofile   100000
cassandra   hard   nofile   100000
cassandra   soft   nproc    32768
cassandra   hard   nproc    32768
cassandra   soft   stack    10240
cassandra   hard   stack    32768
cassandra   hard   memlock  unlimited
cassandra   soft   memlock  unlimited

EOF
cat /tmp/h/a
cassandra   soft   nofile   100000
cassandra   hard   nofile   100000
.
.
.

# replace STRING1 to STRING2 if line contain STRING3
for i in $(cat STRING_LIST) ; do sed -i "/${i}/s/STRING1 /STRING2 /" FILE_U_WANT_TO_MODIFY  ; done

for i in $(cat ip) ; do sed -i "/${i}/s/host /#host /" 184.conf  ; done
# cat ip
10.1.112.34
10.1.112.35
10.1.120.210

while read p; do  sed -i "/${p}/d"  FILE.TXT ; done < STRING.TXT

sed '/STRINGS/d' FILE.TXT

while read p; do  sed "/${p}/s/host /#host /g" FILE1.TXT; done < STRING.TXT   |grep IPADDRESS

sort by 3rd field, separator=":"
sort -k3 -t:

sed 's/[()]//g': remove "()"

cat /etc/passwd|sed 's/qemu/& and kvm/'

sed '5!d' FILE
awk 'NR==5' FILE

sed remove line if pattern matched
sed -i '/pattern/d' file

# vim delete all line
:0,$d

# sed replacing string
grep -R gpgcheck /etc/yum.repos.d/* |awk -F: '{print $1}' |xargs sed -i 's/gpgcheck\=1/gpgcheck\=0/g'

-b, --ignore-leading-blanks  ignore leading blanks
-d, --dictionary-order   consider only blanks and alphanumeric characters
-f, --ignore-case    fold lower case to upper case characters
-g, --general-numeric-sort  compare according to general numerical value
-i, --ignore-nonprinting   consider only printable characters
-M, --month-sort compare  (unknown) < 'JAN' < ... < 'DEC'
-h, --human-numeric-sort  compare human readable numbers (e.g., 2K 1G)
-n, --numeric-sort    compare according to string numerical value
-R, --random-sort    sort by random hash of keys
--random-source=FILE   get random bytes from FILE
-r, --reverse     reverse the result of comparisons
--sort=WORD    sort according to WORD:
-V, --version-sort    natural sort of (version) numbers within text
-u, --unique     with -c, check for strict ordering;

ls
-c: sort by ctime
-r: reverse
-t: sort by mtime
-u:sort by access time?
-X: sort by alphabetically