Sponsored Content
Top Forums Shell Programming and Scripting Incrementing with a twist - please help Post 302400821 by alister on Thursday 4th of March 2010 07:42:10 AM
Old 03-04-2010
Hi, rdcwayx

It's not the eval which generates the data; it's brace expansion.

Code:
#Non-numeric example
$ echo f{ee,i,o,um}
fee fi fo fum

#Numeric example
$ echo {0,1}{0,1}{0,1}
000 001 010 011 100 101 110 111

Since the original poster's problem requires a fairly long sequence of digits, for brevity I wanted to avoid:
Code:
echo {0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z}{0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,etc.....

Storing the list in the variable $digits allows me to do that. However, since brace expansion occurs before variable expansion, we need to send the command line through the shell's parser a second time, using eval. Otherwise we just get:
Code:
$ digits=0,1
$ echo {$digits}{$digits}{$digits}
{0,1}{0,1}{0,1}

Instead of:
Code:
$ eval echo {$digits}{$digits}{$digits}
000 001 010 011 100 101 110 111

Note: Brace expansion does not occur if there is no unquoted comma within the braces, so we do not need to quote {$digits}.

A downside to this approach is that if the list of digits is long enough, or if there are many braced terms to expand, the list of resulting words could exceed the command line length limit. In such a case, your approach is superior as it never needs to execute a long command line. Another way around this limitation would be to write it out explicitly in the for loop:
Code:
$ for i in {0,1}{0,1}{0,1}; do echo $i; done
000
001
010
011
100
101
110
111

IMPORTANT: Brace expansion is not a posix-standardized feature, so if that's a concern, my approach is not an option; yours would be the better choice. Also, the order of brace expansion in relation to parameter expansion as described above is BASH specific (which I chose to use for the illustrative examples since it's much more popular than ksh, and because for this particular scenario it's the more complicated case). In pdksh, ksh88, and ksh93, brace expansion occurs after parameter expansion, not before. So, if using a ksh variant, neither the eval nor the echo nor the command substition is necessary (though in this case their presence does not affect the end result); a simple 'for i in {$digits}{$digits}{$digits}' would be sufficient.

Hope that helps. If not, feel free to ask for clarification.

Cheers,
Alister

Last edited by alister; 03-04-2010 at 09:44 AM..
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

how do I log into this machine - with a twist...

I know this topic has been covered in one form or another, but it hasn't been covered to handle my problem. I was given a Sparc4 running Solaris 2.5.1 The root password is unknown. This machine has no cdrom drive and it has no floppy drive. I tried booting into the single user mode, but... (1 Reply)
Discussion started by: xyyz
1 Replies

2. Shell Programming and Scripting

Compare 2 files yet again but with a twist

Ok so I have a file which contains 2 columns/fields and I have another file with 2 columns. The files look like: file1: 1 33 5 345 18 2 45 1 78 31 file2: 1 c1d2t0 2 c1d3t0 3 c1d4t0 4 c1d4t0 5 c2d1t0 6 c2d1t0 7 c2d1t0 8 c2d1t0 9 c2d1t0 10 c2d1t0 (11 Replies)
Discussion started by: Autumn Tree
11 Replies

3. UNIX for Advanced & Expert Users

building a kernel (with a twist)

Hey all, I am working on a static analysis tool and I wan't to see if it can find bugs in the linux kernel, it uses LLVM framework to analyse the instructions. Long story short I need to build the kernel with a custom compiler. The compiler will create byte code files where binaries usually... (2 Replies)
Discussion started by: zigga15
2 Replies

4. UNIX for Dummies Questions & Answers

file count with a twist

Hello Everyone, I am using the korn shell. I was hoping to find a set of commands to count files in a directory. I am using: ls /home/name/abc* | wc -l This command works fine when a file matches abc* (returns only the file count) , however when no file(s) are found I get... (2 Replies)
Discussion started by: robert4732
2 Replies

5. Shell Programming and Scripting

How to merge two files with a slight twist

Hi, a brief introduction on the soundex python module(english sound comparison): import soundex.py a = "neu yorkk" b = "new york city" print soundex.sound_similar(a, b) output: 1 Suppose I want to merge two files, called mergeleft.csv and mergeright.csv Mergeleft.csv: ... (0 Replies)
Discussion started by: grossgermany
0 Replies

6. Shell Programming and Scripting

Delete duplicate lines... with a twist!

Hi, I'm sorry I'm no coder so I came here, counting on your free time and good will to beg for spoonfeeding some good code. I'll try to be quick and concise! Got file with 50k lines like this: "Heh, heh. Those darn ninjas. They're _____."*wacky The "canebrake", "timber" & "pygmy" are types... (7 Replies)
Discussion started by: shadowww
7 Replies

7. Shell Programming and Scripting

Simple two file compare with twist

I have file1 and file2 I lookup field3 from file2 in field1 of file1 and if there is a match, output field 2,3,5 from file2. I now want to add field2 of file1 in the output. I suspect what I have to do is read the entire line of file1 into a 2 dim array? pls help. here is my code: ... (9 Replies)
Discussion started by: jack.bauer
9 Replies

8. Shell Programming and Scripting

Section Removal With sed; and With a Twist . . .

Hello folks! Raised a bump on my head trying to figure this one out ;) I have an xml file which needs to be edited, removing an entire property section in the work. Here's what the target section layout looks like: <property name="something"> {any number of lines go here} </property>... (7 Replies)
Discussion started by: LinQ
7 Replies

9. Shell Programming and Scripting

Simple two file compare with twist

I have file1 and file2 I lookup field3 from file2 in field1 of file1 and if there is a match, output field 2,3,5 from file2. I now want to add field2 of file1 in the output. I suspect what I have to do is read the entire line of file1 into a 2 dim array? pls help. (1 Reply)
Discussion started by: tmonk1
1 Replies

10. Shell Programming and Scripting

File Listing, with a Twist?

Greetings! I have a quick question which must be deferred to those with greater skill than myself :) In this situation, I wish to create a list of all the files on an entire partition in descending order sorted by date. I tried numerous switches for ls, and found this line to be the closest... (4 Replies)
Discussion started by: LinQ
4 Replies
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 will be 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, will be invoked if the user calls echo without a full pathname. See shell_builtins(1). sh's echo, ksh's echo, and /usr/bin/echo understand the back-slashed escape charac- ters, except that sh's echo does not understand a as the alert character. In addition, ksh's echo, does not have an -n option. sh's echo and /usr/bin/echo only have an -n option if the SYSV3 environment variable is set (see ENVIRONMENT VARIABLES below). If it is, none of the backslashed characters mentioned above are available. csh's echo and /usr/ucb/echo, on the other hand, have an -n option, but do not under- stand the back-slashed escape characters. OPERANDS
The following operand is supported: string A string to be written to standard output. If any operand is "-n", it will be treated as a string, not an option. The following character sequences will be 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. 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 |Standard | +-----------------------------+-----------------------------+ SEE ALSO
echo(1B), printf(1), shell_builtins(1), tr(1), wc(1), 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' will print the phrase WARNING: and sound 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"0337 | od -xc produces: df0a (hex) 337 (ascii) 3 digits Correct: echo "00337" | od -xc produces: lb37 0a00 (hex) 033 7 (ascii) For the octal equivalents of each character, see ascii(5). SunOS 5.10 20 Jan 2000 echo(1)
All times are GMT -4. The time now is 04:47 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy