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Top Forums Shell Programming and Scripting How to handle variable with special character? Post 303026210 by bakunin on Wednesday 21st of November 2018 05:49:04 PM
Old 11-21-2018
Quote:
Originally Posted by green_k
the variable is "v$xyz",
No, it is not. A "variable" is something like "$name" or "${name}", where "name" is a name you choose. "$xyz" might be a variable, but "v$xyz" is a literal "v" followed by the content of a variable with the name "xyz".

Quote:
Originally Posted by green_k
the file name like v$xyz_xxxx_xxxx.txt.
OK, but is the "$xyz" in this filename now meant literally or should that signify the variable portion of the filename which you want to transport via the variable? If the first is the case a simple quotation will suffice, because this is what it is for - inside of (single) quotes the "$" loses its special meaning to the shell and reverts back to a normal character:

Code:
ls -l v$xyz_xxxx_xxxx.txt

will first replace "$xyz_xxxx_xxxx" with the content of a variable named "xyz_xxxx_xxxx" (which most probably will not exist so that it evaluates to "", the empty string) and therefore search for a file named "v.txt". Whereas:

Code:
ls -l 'v$xyz_xxxx_xxxx.txt'

(notice the single quotes) will look for a file named exactly this: "v$xyz_xxxx_xxxx.txt".

If "$xyz" is a variable and you want to use that as the changing part of an otherwise fixed filename then this code snippet is for you:

Code:
xyz="some$thing"
ls -l "v${xyz}_xxxx_xxxx.txt"

This will search for a file name "vsome$thing_xxxx_xxxx.txt". Because of the braces around "xyz" the shell knows that only this (and not the rest of the string) is the name of the variable. Notice the double quotes: you should habitually double-quote every use of any variable - ever and always! (There are only very few exceptions to this rule of thumb.) This way blanks (yes, filename can contain blanks) will not break your script.

I hope this helps.

bakunin
 

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read(1) 							   User Commands							   read(1)

NAME
read - read a line from standard input SYNOPSIS
/usr/bin/read [-r] var... sh read name... csh set variable = $< ksh read [ -prsu [n]] [ name ? prompt] [name...] DESCRIPTION
/usr/bin/read The read utility will read a single line from standard input. By default, unless the -r option is specified, backslash () acts as an escape character. If standard input is a terminal device and the invoking shell is interactive, read will prompt for a continuation line when: o The shell reads an input line ending with a backslash, unless the -r option is specified. o A here-document is not terminated after a NEWLINE character is entered. The line will be split into fields as in the shell. The first field will be assigned to the first variable var, the second field to the second variable var, and so forth. If there are fewer var operands specified than there are fields, the leftover fields and their interven- ing separators will be assigned to the last var. If there are fewer fields than vars, the remaining vars will be set to empty strings. The setting of variables specified by the var operands will affect the current shell execution environment. If it is called in a subshell or separate utility execution environment, such as one of the following: (read foo) nohup read ... find . -exec read ... ; it will not affect the shell variables in the caller's environment. The standard input must be a text file. sh One line is read from the standard input and, using the internal field separator, IFS (normally space or tab), to delimit word boundaries, the first word is assigned to the first name, the second word to the second name, and so on, with leftover words assigned to the last name. Lines can be continued using ewline. Characters other than NEWLINE can be quoted by preceding them with a backslash. These backslashes are removed before words are assigned to names, and no interpretation is done on the character that follows the backslash. The return code is 0, unless an end-of-file is encountered. csh The notation: set variable = $< loads one line of standard input as the value for variable. (See csh(1)). ksh The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators. The escape character, (), is used to remove any special meaning for the next character and for line continuation. In raw mode, -r, the character is not treated specially. The first field is assigned to the first name, the second field to the second name, and so on, with leftover fields assigned to the last name. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using |&. If the -s flag is present, the input will be saved as a command in the history file. The flag -u can be used to specify a one digit file descriptor unit n to read from. The file descriptor can be opened with the exec special command. The default value of n is 0. If name is omitted, REPLY is used as the default name. The exit status is 0 unless the input file is not open for reading or an end-of-file is encoun- tered. An end-of-file with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a ?, the remainder of this word is used as a prompt on standard error when the shell is interactive. The exit status is 0 unless an end-of- file is encountered. OPTIONS
The following option is supported: -r Does not treat a backslash character in any special way. Considers each backslash to be part of the input line. OPERANDS
The following operand is supported: var The name of an existing or non-existing shell variable. EXAMPLES
Example 1: An example of the read command The following example for /usr/bin/read prints a file with the first field of each line moved to the end of the line: example% while read -r xx yy do printf "%s %s " "$yy" "$xx" done < input_file ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of read: LANG, LC_ALL, LC_CTYPE, LC_MES- SAGES, and NLSPATH. IFS Determines the internal field separators used to delimit fields. PS2 Provides the prompt string that an interactive shell will write to standard error when a line ending with a backslash is read and the -r option was not specified, or if a here-document is not terminated after a newline character is entered. EXIT STATUS
The following exit values are returned: 0 Successful completion. >0 End-of-file was detected or an error occurred. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
csh(1), ksh(1), line(1), set(1), sh(1), attributes(5), environ(5), standards(5) SunOS 5.10 28 Mar 1995 read(1)
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