Why is the dd command called "dd" ?
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dd = convert and copy command, but as c compile (cc) was already used it was decided to shift up the alphabet for the 'convert and copy' command.
Second video https://catonmat.net/why-unix-commands-are-short 30:40
Unix Trivia
Unix Trivia
Last edited by rufwoof on Fri 08 Nov 2019, 10:37, edited 1 time in total.
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It actually comes from the IBM Job Control Language for batch processing.
The following example, using JCL, DD is used to copy a file on OS/360:
The following example, using JCL, DD is used to copy a file on OS/360:
Code: Select all
//IS198CPY JOB (IS198T30500),'COPY JOB',CLASS=L,MSGCLASS=X
//COPY01 EXEC PGM=IEBGENER
//SYSPRINT DD SYSOUT=*
//SYSUT1 DD DSN=OLDFILE,DISP=SHR
//SYSUT2 DD DSN=NEWFILE,
// DISP=(NEW,CATLG,DELETE),
// SPACE=(CYL,(40,5),RLSE),
// DCB=(LRECL=115,BLKSIZE=1150)
//SYSIN DD DUMMY
Code: Select all
# dd --helpUsage: dd [OPERAND]...
or: dd OPTION
Copy a file, converting and formatting according to the operands.
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jfadmin No it doesn't.
The DD statement in JCL stands for Data Definition and has nothing whatsoever to do with copying.
The program IEBGENER is the thing that does the copying.
SYSUT1 is the source file
and SYSUT2 is the target file
in your example.
The DD statement in JCL stands for Data Definition and has nothing whatsoever to do with copying.
The program IEBGENER is the thing that does the copying.
SYSUT1 is the source file
and SYSUT2 is the target file
in your example.
"Just think of it as leaving early to avoid the rush" - T Pratchett
https://en.wikipedia.org/wiki/Dd_(Unix)#HistoryBurn_IT wrote:jfadmin No it doesn't.
The DD statement in JCL stands for Data Definition and has nothing whatsoever to do with copying.
The program IEBGENER is the thing that does the copying.
SYSUT1 is the source file
and SYSUT2 is the target file
in your example.
Read what I said!
I said IN JCL
The dd statement in JCL is used to link a logical filename in a program to a physical data stream somewhere in the real world.
It has nothing to do with what that data is used for, though it may tell the operating system what state to leave that data in when it is finished with it.
I said IN JCL
The dd statement in JCL is used to link a logical filename in a program to a physical data stream somewhere in the real world.
It has nothing to do with what that data is used for, though it may tell the operating system what state to leave that data in when it is finished with it.
"Just think of it as leaving early to avoid the rush" - T Pratchett
http://ibmmainframes.com/about9267.htmlBurn_IT wrote:Read what I said!
I said IN JCL
The dd statement in JCL is used to link a logical filename in a program to a physical data stream somewhere in the real world.
It has nothing to do with what that data is used for, though it may tell the operating system what state to leave that data in when it is finished with it.
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And your point is??
In all those examples there is a program involved to do the copying.
Even if you do want to use JCL to do things like allocate space for a file or catalogue a file, you still have to have a "PGM" statement (an executable program).
The most used program for this is IEFBR14 which consists of just a return statement.
In those examples the program is the sort utility.
In all those examples there is a program involved to do the copying.
Even if you do want to use JCL to do things like allocate space for a file or catalogue a file, you still have to have a "PGM" statement (an executable program).
The most used program for this is IEFBR14 which consists of just a return statement.
In those examples the program is the sort utility.
"Just think of it as leaving early to avoid the rush" - T Pratchett
Digressing somewhat but still on OT..
How many know what the .tar extension stands for?
Tape Archive.
Of course if you are over 35 or so and in IT or are a coder you knew this, no?
How many know what the .tar extension stands for?
Tape Archive.
Of course if you are over 35 or so and in IT or are a coder you knew this, no?
Puppy Linux Blog - contact me for access
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my very first computer program was line by line on punch cards...written in FORTRAN and ran on an IBM mainframe in 1974 at AVCO Lycoming, a gas turbine engine manufacturer. My dad was an engineer working on the AGT 1500 engine that eventually ended up in the Abrams M1A1 main battle tank.
He arranged that I could drop off the pack of cards in the correct order to the high priests (sysop's) who would at some point take my program from the queue and run it. Next day my dad brought home a printout of the results.
I was 13 years old and the program did not do much..more of a "Hello World" but it ran. Only the sysop's had direct access...the computer room was climate controlled high security area...no one could even look at it except those guys.
I later went to school to be a mainframe sysop and batch script programmer...but it was already the dawn of the new age and LAN's and the desktop computer workstation was on the horizon.
He arranged that I could drop off the pack of cards in the correct order to the high priests (sysop's) who would at some point take my program from the queue and run it. Next day my dad brought home a printout of the results.
I was 13 years old and the program did not do much..more of a "Hello World" but it ran. Only the sysop's had direct access...the computer room was climate controlled high security area...no one could even look at it except those guys.
I later went to school to be a mainframe sysop and batch script programmer...but it was already the dawn of the new age and LAN's and the desktop computer workstation was on the horizon.