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Top Forums Shell Programming and Scripting Capture first N Bytes from first line in a file Post 302349126 by sharadpisal on Monday 31st of August 2009 07:18:48 AM
Old 08-31-2009
if : input file
of : output file
ibs : tell how many bytes to read at a time, something like block size
count: read those blocks for maximum of this times,

so


# dd if=infile ibs=N count=M of=outfile
Will work if N * M = 48
 

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DDRESCUE(1)							   User Commands						       DDRESCUE(1)

NAME
ddrescue - data recovery tool SYNOPSIS
ddrescue [options] infile outfile [logfile] DESCRIPTION
GNU ddrescue - Data recovery tool. Copies data from one file or block device to another, trying hard to rescue data in case of read errors. You should use a logfile unless you know what you are doing. OPTIONS
-h, --help display this help and exit -V, --version output version information and exit -a, --min-read-rate=<bytes> minimum read rate of good areas in bytes/s -A, --try-again mark non-split, non-trimmed blocks as non-tried -b, --block-size=<bytes> sector size of input device [default 512] -B, --binary-prefixes show binary multipliers in numbers [SI] -c, --cluster-size=<sectors> sectors to copy at a time [128] -C, --complete-only do not read new data beyond logfile limits -d, --direct use direct disc access for input file -D, --synchronous use synchronous writes for output file -e, --max-errors=[+]<n> maximum number of [new] error areas allowed -E, --max-error-rate=<bytes> maximum allowed rate of read errors per second -f, --force overwrite output device or partition -F, --fill=<types> fill given type blocks with infile data (?*/-+) -g, --generate-logfile generate approximate logfile from partial copy -i, --input-position=<bytes> starting position in input file [0] -I, --verify-input-size verify input file size with size in logfile -K, --skip-size=<bytes> initial size to skip on read error [64 KiB] -m, --domain-logfile=<file> restrict domain to finished blocks in file -M, --retrim mark all failed blocks as non-trimmed -n, --no-split do not try to split or retry failed blocks -o, --output-position=<bytes> starting position in output file [ipos] -p, --preallocate preallocate space on disc for output file -q, --quiet suppress all messages -r, --max-retries=<n> exit after given retries (-1=infinity) [0] -R, --reverse reverse direction of copy operations -s, --max-size=<bytes> maximum size of input data to be copied -S, --sparse use sparse writes for output file -t, --truncate truncate output file to zero size -T, --timeout=<interval> maximum time since last successful read -v, --verbose be verbose (a 2nd -v gives more) -x, --extend-outfile=<bytes> extend outfile size to be at least this long Numbers may be followed by a multiplier: b = blocks, k = kB = 10^3 = 1000, Ki = KiB = 2^10 = 1024, M = 10^6, Mi = 2^20, G = 10^9, Gi = 2^30, etc... Time intervals have the format 1[.5][smhd] or 1/2[smhd]. REPORTING BUGS
Report bugs to bug-ddrescue@gnu.org Ddrescue home page: http://www.gnu.org/software/ddrescue/ddrescue.html General help using GNU software: http://www.gnu.org/gethelp COPYRIGHT
Copyright (C) 2012 Antonio Diaz Diaz. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
The full documentation for ddrescue is maintained as a Texinfo manual. If the info and ddrescue programs are properly installed at your site, the command info ddrescue should give you access to the complete manual. ddrescue 1.16 June 2012 DDRESCUE(1)
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