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Top Forums Shell Programming and Scripting How to insert a '#' in the first position of all the files? Post 302842869 by Don Cragun on Saturday 10th of August 2013 11:15:00 PM
Old 08-11-2013
When you use the $(command) and `command` forms of command substitution, the trailing <newline> character (if there is one) will be dropped from the output. There doesn't seem to be any need to assign the output of sed to a variable; just let sed write directly into your output file. The following would seem to do what you want:
Code:
sed 's/.*song=good.*/\#&/' $(cat /bin/user/input_file.txt) > /bin/user/new/output_file.txt

This should work on any Linux or UNIX System as long as you are using a shell (such as a Korn shell [ksh] or bash) that recognizes minimal requirements specified by the POSIX standards and the Single UNIX Specifications as long as the pathnames stored in input_file.txt do not contain any whitespace characters.

Note also that using:
Code:
echo $b

to print a line of output will produce different output when using different versions of echo if the variable b contains any tab characters, any occurrences of multiple adjacent spaces, starts with a minus sign, or contains any backslash characters. If you want to copy the contents of a variable to a file adding a <newline> character to the end of it (without altering spacing, leading minus signs, and backslash characters), you could replace the echo command with:
Code:
printf "%s\n" "$b"

And, finally, note that using:
Code:
echo $b > /bin/user/new/output_file.txt

will only save the output from the last file processed. Each time you use > as a redirection operator in the shell, all previous output in the destination file will be replaced.
 

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echo(1) 							   User Commands							   echo(1)

NAME
echo - echo arguments SYNOPSIS
/usr/bin/echo [string]... DESCRIPTION
The echo utility writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output. If there are no arguments, only the NEWLINE character is written. echo is useful for producing diagnostics in command files, for sending known data into a pipe, and for displaying the contents of environ- ment variables. The C shell, the Korn shell, and the Bourne shell all have echo built-in commands, which, by default, is invoked if the user calls echo without a full pathname. See shell_builtins(1). sh's echo, ksh's echo, ksh93's echo, and /usr/bin/echo understand the back-slashed escape characters, except that sh's echo does not understand a as the alert character. In addition, ksh's and ksh93's echo does not have an -n option. sh's echo and /usr/bin/echo have an -n option if the SYSV3 environment variable is set (see ENVIRONMENT VARIABLES below). csh's echo and /usr/ucb/echo, on the other hand, have an -n option, but do not understand the back-slashed escape characters. sh and ksh deter- mine whether /usr/ucb/echo is found first in the PATH and, if so, they adapt the behavior of the echo builtin to match /usr/ucb/echo. OPERANDS
The following operand is supported: string A string to be written to standard output. If any operand is "-n", it is treated as a string, not an option. The following char- acter sequences is recognized within any of the arguments: a Alert character.  Backspace. c Print line without new-line. All characters following the c in the argument are ignored. f Form-feed. New-line. Carriage return. Tab. v Vertical tab. \ Backslash. n Where n is the 8-bit character whose ASCII code is the 1-, 2- or 3-digit octal number representing that character. USAGE
Portable applications should not use -n (as the first argument) or escape sequences. The printf(1) utility can be used portably to emulate any of the traditional behaviors of the echo utility as follows: o The Solaris 2.6 operating environment or compatible version's /usr/bin/echo is equivalent to: printf "%b " "$*" o The /usr/ucb/echo is equivalent to: if [ "X$1" = "X-n" ] then shift printf "%s" "$*" else printf "%s " "$*" fi New applications are encouraged to use printf instead of echo. EXAMPLES
Example 1 Finding how far below root your current directory is located You can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows: o Echo your current-working-directory's full pathname. o Pipe the output through tr to translate the path's embedded slash-characters into space-characters. o Pipe that output through wc -w for a count of the names in your path. example% /usr/bin/echo $PWD | tr '/' ' ' | wc -w See tr(1) and wc(1) for their functionality. Below are the different flavors for echoing a string without a NEWLINE: Example 2 /usr/bin/echo example% /usr/bin/echo "$USER's current directory is $PWDc" Example 3 sh/ksh shells example$ echo "$USER's current directory is $PWDc" Example 4 csh shell example% echo -n "$USER's current directory is $PWD" Example 5 /usr/ucb/echo example% /usr/ucb/echo -n "$USER's current directory is $PWD" ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of echo: LANG, LC_ALL, LC_CTYPE, LC_MES- SAGES, and NLSPATH. SYSV3 This environment variable is used to provide compatibility with INTERACTIVE UNIX System and SCO UNIX installation scripts. It is intended for compatibility only and should not be used in new scripts. This variable is applicable only for Solaris x86 platforms, not Solaris SPARC systems. EXIT STATUS
The following error values are returned: 0 Successful completion. >0 An error occurred. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |CSI |Enabled | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
ksh93(1), printf(1), shell_builtins(1), tr(1), wc(1), echo(1B), ascii(5), attributes(5), environ(5), standards(5) NOTES
When representing an 8-bit character by using the escape convention n, the n must always be preceded by the digit zero(0). For example, typing: echo 'WARNING:7' prints the phrase WARNING: and sounds the "bell" on your terminal. The use of single (or double) quotes (or two backslashes) is required to protect the "" that precedes the "07". Following the , up to three digits are used in constructing the octal output character. If, following the n, you want to echo addi- tional digits that are not part of the octal representation, you must use the full 3-digit n. For example, if you want to echo "ESC 7" you must use the three digits "033" rather than just the two digits "33" after the . 2 digits Incorrect: echo "337" | od -xc produces: df0a (hex) 337 (ascii) 3 digits Correct: echo "0337" | od -xc produces: lb37 0a00 (hex) 033 7 (ascii) For the octal equivalents of each character, see ascii(5). SunOS 5.11 8 Apr 2008 echo(1)
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