You can "test" a lot of conditions with the shell built-in command "test".
If you have a look at the man/help page, it should tell you all of the available comparisons/tests.
Code:
man test
or
Code:
help test
Here is what I got from typing in "help test" at a Bash shell prompt:
Code:
$ help test
test: test [expr]
Exits with a status of 0 (true) or 1 (false) depending on
the evaluation of EXPR. Expressions may be unary or binary. Unary
expressions are often used to examine the status of a file. There
are string operators as well, and numeric comparison operators.
File operators:
-a FILE True if file exists.
-b FILE True if file is block special.
-c FILE True if file is character special.
-d FILE True if file is a directory.
-e FILE True if file exists.
-f FILE True if file exists and is a regular file.
-g FILE True if file is set-group-id.
-h FILE True if file is a symbolic link.
-L FILE True if file is a symbolic link.
-k FILE True if file has its `sticky' bit set.
-p FILE True if file is a named pipe.
-r FILE True if file is readable by you.
-s FILE True if file exists and is not empty.
-S FILE True if file is a socket.
-t FD True if FD is opened on a terminal.
-u FILE True if the file is set-user-id.
-w FILE True if the file is writable by you.
-x FILE True if the file is executable by you.
-O FILE True if the file is effectively owned by you.
-G FILE True if the file is effectively owned by your group.
-N FILE True if the file has been modified since it was last read.
FILE1 -nt FILE2 True if file1 is newer than file2 (according to
modification date).
FILE1 -ot FILE2 True if file1 is older than file2.
FILE1 -ef FILE2 True if file1 is a hard link to file2.
String operators:
-z STRING True if string is empty.
-n STRING
STRING True if string is not empty.
STRING1 = STRING2
True if the strings are equal.
STRING1 != STRING2
True if the strings are not equal.
STRING1 < STRING2
True if STRING1 sorts before STRING2 lexicographically.
STRING1 > STRING2
True if STRING1 sorts after STRING2 lexicographically.
Other operators:
-o OPTION True if the shell option OPTION is enabled.
! EXPR True if expr is false.
EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.
arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.
Arithmetic binary operators return true if ARG1 is equal, not-equal,
less-than, less-than-or-equal, greater-than, or greater-than-or-equal
than ARG2.
Hope this helps for future questions on comparisons and tests using the shell.
Hi Friends,
Can any of you explain me about the below line of code?
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Im not able to understand, what exactly it is doing :confused:
Any help would be useful for me.
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Discussion started by: penchev
3 Replies
LEARN ABOUT OPENDARWIN
test
TEST(1) BSD General Commands Manual TEST(1)NAME
test, [ -- condition evaluation utility
SYNOPSIS
test expression
[ expression ]
DESCRIPTION
The test utility evaluates the expression and, if it evaluates to true, returns a zero (true) exit status; otherwise it returns 1 (false).
If there is no expression, test also returns 1 (false).
All operators and flags are separate arguments to the test utility.
The following primaries are used to construct expression:
-b file True if file exists and is a block special file.
-c file True if file exists and is a character special file.
-d file True if file exists and is a directory.
-e file True if file exists (regardless of type).
-f file True if file exists and is a regular file.
-g file True if file exists and its set group ID flag is set.
-h file True if file exists and is a symbolic link. This operator is retained for compatibility with previous versions of this pro-
gram. Do not rely on its existence; use -L instead.
-k file True if file exists and its sticky bit is set.
-n string True if the length of string is nonzero.
-p file True if file is a named pipe (FIFO).
-r file True if file exists and is readable.
-s file True if file exists and has a size greater than zero.
-t file_descriptor
True if the file whose file descriptor number is file_descriptor is open and is associated with a terminal.
-u file True if file exists and its set user ID flag is set.
-w file True if file exists and is writable. True indicates only that the write flag is on. The file is not writable on a read-only
file system even if this test indicates true.
-x file True if file exists and is executable. True indicates only that the execute flag is on. If file is a directory, true indi-
cates that file can be searched.
-z string True if the length of string is zero.
-L file True if file exists and is a symbolic link.
-O file True if file exists and its owner matches the effective user id of this process.
-G file True if file exists and its group matches the effective group id of this process.
-S file True if file exists and is a socket.
file1 -nt file2
True if file1 exists and is newer than file2.
file1 -ot file2
True if file1 exists and is older than file2.
file1 -ef file2
True if file1 and file2 exist and refer to the same file.
string True if string is not the null string.
s1 = s2 True if the strings s1 and s2 are identical.
s1 != s2 True if the strings s1 and s2 are not identical.
s1 < s2 True if string s1 comes before s2 based on the ASCII value of their characters.
s1 > s2 True if string s1 comes after s2 based on the ASCII value of their characters.
s1 True if s1 is not the null string.
n1 -eq n2 True if the integers n1 and n2 are algebraically equal.
n1 -ne n2 True if the integers n1 and n2 are not algebraically equal.
n1 -gt n2 True if the integer n1 is algebraically greater than the integer n2.
n1 -ge n2 True if the integer n1 is algebraically greater than or equal to the integer n2.
n1 -lt n2 True if the integer n1 is algebraically less than the integer n2.
n1 -le n2 True if the integer n1 is algebraically less than or equal to the integer n2.
These primaries can be combined with the following operators:
! expression True if expression is false.
expression1 -a expression2
True if both expression1 and expression2 are true.
expression1 -o expression2
True if either expression1 or expression2 are true.
(expression) True if expression is true.
The -a operator has higher precedence than the -o operator.
Some shells may provide a builtin test command which is similar or identical to this utility. Consult the builtin(1) manual page.
GRAMMAR AMBIGUITY
The test grammar is inherently ambiguous. In order to assure a degree of consistency, the cases described in the IEEE Std 1003.2
(``POSIX.2''), section D11.2/4.62.4, standard are evaluated consistently according to the rules specified in the standards document. All
other cases are subject to the ambiguity in the command semantics.
RETURN VALUES
The test utility exits with one of the following values:
0 expression evaluated to true.
1 expression evaluated to false or expression was missing.
>1 An error occurred.
SEE ALSO builtin(1), expr(1), sh(1)STANDARDS
The test utility implements a superset of the IEEE Std 1003.2 (``POSIX.2'') specification.
BSD May 31, 1993 BSD