replace file extensions

 # change .htm files to .html

 for file in *.htm ; do mv $file `echo $file | sed 's/\(.*\.\)htm/\1html/'` ; done

 # change .html files to .htm

 for file in *.html ; do mv $file `echo $file | sed 's/\(.*\.\)html/\1htm/'` ; done

 #change .html files to .shtml

 for file in *.html ; do mv $file `echo $file | sed 's/\(.*\.\)html/\1shtml/'` ; done

 #change .html files to php

 for file in *.html ; do mv $file `echo $file | sed 's/\(.*\.\)html/\1php/'` ; done

 replace string in text

 :%s/str1/str2/gc  整个文档

 :1,$s/str1/str2/gc  整个文档

 :.,$s/str1/str2/gc  从当前到结尾  

 #extract a range of lines from a text

 sed -n 16224,16482p filename > newfile

 sed -n -e 12345p filename > newfile

 sed '5!d' filename > newfile

 # compare substring of a field

 awk '{if ( substr($1,0,7)>6435201 && substr($1,0,7)<6521605) print $0}'

 # find a file

 find ./ -name 'my*'

 # find & cp

 find /PATH/TO/YOUR/FILES -name NAME.EXT -exec cp -rfp {} /DST_DIR \;

 # add numbers in a bash script

 num=$((num1 + num2))

 num=$(($num1 + $num2))       # also works

 num=$((num1 + 2 + 3))        # ...

 num=$[num1+num2]             # old, deprecated arithmetic expression syntax

 # Assign Output of Shell Command To Variable

 var=$(command-name-here)

 var=$(command-name-here arg1)

 var=$(/path/to/command)

 var=$(/path/to/command arg1 arg2)

 var=`command-name-here`

 var=`command-name-here arg1`

 var=`/path/to/command`

 var=`/path/to/command arg1 arg2`

 # fg/bg/nohup

 find /etc/httpd/ -name "httpd.conf" -print >find.dt 2>&1 & 

 awk '{if ($11=="9002" && $6==0) {revenue+=$3;count++}}END{print revenue;print count}' new_ck_table

 awk '{if ($3=="+1") count++;}END{print count;}' file.txt

 awk 'FNR==NR{a[$1]=1; next}; {if($1 in a) print $0} ' rank02.dat 0201-all.tmp3   >  rank02.tmp3

 # output third column to end of each row

 cut -d ":" -f 3-

 # filter empty lines

 grep -e '^$' -v 

 # comment /uncomment

 ctrl+v -> x

 ctrl+v -> shift+i # esc

 # sort by one column

 sort -k 1 0316.new -o 0316.new 

 # remove leading space

 sed -e 's/^[ \t]*//'

 # mount NFS

 mount -t nfs 10.134.12.60:/data/online/public localDir

 ##--------------- high frequency python command ------------------------ 

 # regex

 text = "<H1>title</H1>"

 re.mathc('<.*>', text) # match <H1>title</H1>

 re.match('<.*?>',text)  # match <H1>

 # sum of elements in a list

 sum = reduce(lambda x,y: x+y, mylist)

 # compare all elements in two lists

 if all(x==y for x, y in zip(X, Y))

     do something

 # get sorted dictionary by key

 sorted(dd.keys())

 [(key, dd[key]) for key in sorted(dd.keys())]

 print ' '.join([str(key)+':'+str(dd[key]) for key in sorted(dd.keys())])

 # get sorted dictionary by value

 [key for key in sorted(dd, key=dd.get, reverse=True)]

 [(key, dd[key]) for key in sorted(dd, key=dd.get, reverse=True)]

 print ' '.join([str(key)+':'+str(dd[key]) for key in sorted(dd, key=dd.get, reverse=True)])

 sorted(myDict.items(), key=lambda e: e[1][2]) # value is a list

 # get key intersection of two dictionaries

 intersect = set(dict_A.keys()) & set(dict_B.keys()) 

 # sort a list of tuple

 sorted_list = sorted(tuples, key=lambda x:x[0])

 # map list onto dictionary

 mydict = {x.split(':')[0]:x.split(':')[1] for x in mylist} 

 from os.path import basename

 from os.path import splitext

 fname = splitext(basename(fullname))[0]

 # sort list and return index of list

 sorted_index = sorted(range(len(list)), key=lambda k: list[k])

 # intersection of two lists

 b1 = [...]

 b2 = [...]

 intersection = set(b1).intersection(b2)

 # string to date / date to string

 import  datetime

 obj_date = datetime.datetime.strptime(str_date, "%Y%m%d%H%M").date()

 str_date = obj_date.strftime('%Y%m%d%H%M')

 obj_date =  obj_date + datetime.timedelta(days=-1)

 # date to timestamp

 time.mktime(time.strptime('2015-03-15 00:00:00', '%Y-%m-%d %H:%M:%S'))

 # read first N line of a file

 with open("datafile") as myfile:

     head = [next(myfile) for x in xrange(N)]

 print head

# remove leading whitespace in vim

%s/^\s*//g