Use format if conditional statement:
1, a single branch statements
if condition; then
execute the statement
Fi
2, double branch statements
if condition; then
execute statement 1
the else
execute statements 2
Fi
. 3, multi-branch statements
if condition; then
execute the statement . 1
elif; the then
execute the statement 2
elif; the then
executing the statement. 3
the else
execute the statement. 4
Fi
Exit
under certain conditions to determine if the condition is not satisfied, we have to manually exit the program, otherwise the code behind can not be executed;
after the completion of the implementation of the code is correct, we have developed the correct exit code exit 0;
#!/bin/bash # Determine whether a file exists if [ $# -lt 1 ]; then echo "At least one argument." exit 1 be if [ -e $1 ];then echo "The file exists" else echo "This file does not exist." if
2, determine whether the current system on the user's default shell bash whether the program, if there is, it shows how many such users, otherwise showed no such users; [and show those users is bash]
#!/bin/bash # Determine the user's default shell type declare -i sum=`grep "bin/bash$" /etc/passwd | wc -l` if grep "/bin/bash$" /etc/passwd &> /dev/null ; then echo "there is $ sum users, shell program to / bin / bash" grep "/bin/bash$" /etc/passwd | cut -d: -f1 exit 0 else echo "no such user" exit 1 be
3, write a script, given a file, for example: / etc / inittab a, to determine whether there is a blank line in the file? b, if so, its line number blank lines displayed, otherwise there is no blank lines
#^[[:space:]]*$ #!/bin/bash # B=`grep -n "^[[:space:]]*$" /etc/inittab | wc -l` C=`grep -n "^[[:space:]]*$" /root/abc | cut -d: -f1` if [ $B -eq 0 ] ; then echo "no blank lines." exit 1 else echo "there is a blank line, blank line behavior $ C" exit 0 be
4, write a script, given a user to determine whether the UID and GID, as if, like, it shows that the user is "good guy", otherwise it is "bad guy"
#!/bin/bash # 1, for doing traversal / etc / passwd for i in $ (cat / etc / passwd); do // sed be completed; 2, is determined for each row UID and GID if [ `cut -d: -f3 $i` = `cut -d: -f4 $i` ];then echo "good guy" exit 0 else echo "bad guy" exit 1 be done
5, to determine whether the total entry command history command history is more than 1000, if greater than, "some command will gone" is displayed, otherwise OK
#!/bin/bash
#
S=`history | awk '{print $1}' | tail -1`
if [ $S -gt 1000 ];then
echo "some command will gone"
exit 0
else
echo "OK"
be
6, given a file, if an ordinary file, on the show, if the file is a directory, is also displayed, otherwise it displays "does not recognize"
#!/bin/bash # # input() read -t 5 -p ( "Please enter a file:") filename // -t waiting time echo # default to wrap if [ -n $filename ];then echo "eg. /etc/fstab" exit 8 be if [ -f $filename ]; then echo "$ filename is a regular file." exit 0 elif [ -d $filename ];then echo "$ filename is a directory file" exit 0 else echo "does not recognize" exit 1 be
7, write a script that can accept a parameter (file path) to determine if this parameter is an existing file on the show "ok", otherwise, it displays "No such file"
#!/bin/bash # read -p "Please enter a file path:" filename if [ -e $filename ];then echo "OK" else echo "No such file" be
8, write a script, pass two parameters to the script, and display both the product and the two of
#!/bin/bash # echo $[$1+$2] echo $[$1*$2]