If & whle & case

If & whle & case

if [ 1 -eq 1 ] #expression
then
   #Statement(s) to be executed if expression is true
   echo Yes
fi

© Bash Test Operators

-eq	is equal to
-ne	is not equal to
-gt	is greater than
-ge	is greater than or equal to
-lt	is less than
-le	is less than or equal to
<	is less than
<=	is less than or equal to
>	is greater tha
>=	is greater than or equal to
=	is equal to
==	The == comparison operator behaves differently within a double-brackets test
!=	is not equal to
<	is less than, in ASCII alphabetical order
>	is greater than, in ASCII alphabetical order.
-z	string is null
-n	string is not null.
-e	file exists
-a	is deprecated and its use is discouraged.
-f	file is a regular file (not a directory or device file)
-d	file is a directory
-h	file is a symbolic link
-L	file is a symbolic link
-b	file is a block device
-c	file is a character device
-p	file is a pipe
-S	file is a socket
-s	file is not zero size
-t	file (descriptor) is associated with a terminal device;
-r	file has read permission (for the user running the test)
-w	file has write permission (for the user running the test)
-x	file has execute permission (for the user running the test)
-g	set-group-id (sgid) flag set on file or directory
-u	set-user-id (suid) flag set on file
-k	sticky bit set
-O	you are owner of file
-G	group-id of file same as yours
-N	file modified since it was last read
-nt	file f1 is newer than f2 if [ "$f1" -nt "$f2" ]
-ot	file f1 is older than f2 if [ "$f1" -ot "$f2" ]
-ef	files f1 and f2 are hard links to the same file if [ "$f1" -ef "$f2" ]
!	“not” – reverses the sense of the tests above (returns true if condition absent).

pairwise-compare with if loop

© Ole Tange; 2018

for i in *.txt ; do
  for j in *.txt ; do
    if [ "$i" '<' "$j" ] ; then
      echo "Pairs $i and $j"
    fi
  done
done

字符串判断

##https://blog.csdn.net/Primeprime/article/details/79625306
strA="long string"
strB="string"
result=$(echo $strA | grep "${strB}")
if [[ "$result" != "" ]]
then
  echo "包含"
else
  echo "不包含"
fi

while

while [ expression ]
do
   Statement(s) to be executed if expression is true
done

try

reference:筱光

{ # try

    command1
    #save your output

} || { # except
    # save log for exception
}