What does this IF statement mean

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I have been trying to find online what these if statement mean. Below are a few.



if [ "$snums[k]" != "NA" -a ! -f "$aliases[k].4dfp.img" ]; then
if [ -f "$dcmfile" -a -n "`cat $dcmfile`" ]; then


The -a used in these two examples do not make senses to me.




linux bash




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  • A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
    – Fox
    Jul 10 at 23:20










  • Oh i see. I always thought -a was for checking to see if a file exists.
    – Aaron Tanenbaum
    Jul 11 at 15:41














up vote
1
down vote

favorite












I have been trying to find online what these if statement mean. Below are a few.



if [ "$snums[k]" != "NA" -a ! -f "$aliases[k].4dfp.img" ]; then
if [ -f "$dcmfile" -a -n "`cat $dcmfile`" ]; then


The -a used in these two examples do not make senses to me.




linux bash




share|improve this question





















  • A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
    – Fox
    Jul 10 at 23:20










  • Oh i see. I always thought -a was for checking to see if a file exists.
    – Aaron Tanenbaum
    Jul 11 at 15:41












up vote
1
down vote

favorite









up vote
1
down vote

favorite











I have been trying to find online what these if statement mean. Below are a few.



if [ "$snums[k]" != "NA" -a ! -f "$aliases[k].4dfp.img" ]; then
if [ -f "$dcmfile" -a -n "`cat $dcmfile`" ]; then


The -a used in these two examples do not make senses to me.




linux bash




share|improve this question













I have been trying to find online what these if statement mean. Below are a few.



if [ "$snums[k]" != "NA" -a ! -f "$aliases[k].4dfp.img" ]; then
if [ -f "$dcmfile" -a -n "`cat $dcmfile`" ]; then


The -a used in these two examples do not make senses to me.





linux bash





share|improve this question












share|improve this question




share|improve this question








edited Jul 10 at 20:32









SivaPrasath

3,68311636




3,68311636









asked Jul 10 at 20:20









Aaron Tanenbaum

61




61











  • A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
    – Fox
    Jul 10 at 23:20










  • Oh i see. I always thought -a was for checking to see if a file exists.
    – Aaron Tanenbaum
    Jul 11 at 15:41
















  • A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
    – Fox
    Jul 10 at 23:20










  • Oh i see. I always thought -a was for checking to see if a file exists.
    – Aaron Tanenbaum
    Jul 11 at 15:41















A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
– Fox
Jul 10 at 23:20




A good reason you may not have seen -a or -o is that they have been declared "obsolescent" by POSIX. Script authors are strongly encouraged to use the shell's && and || instead
– Fox
Jul 10 at 23:20












Oh i see. I always thought -a was for checking to see if a file exists.
– Aaron Tanenbaum
Jul 11 at 15:41




Oh i see. I always thought -a was for checking to see if a file exists.
– Aaron Tanenbaum
Jul 11 at 15:41










1 Answer
1






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2
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-a is logical AND. If both the operands are true, then the condition becomes true otherwise false.



-n Checks if the given string operand size is non-zero; if it is nonzero length, then it returns true.






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  • 1




    And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
    – l0b0
    Jul 10 at 21:27










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1 Answer
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1 Answer
1






active

oldest

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active

oldest

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active

oldest

votes








up vote
2
down vote













-a is logical AND. If both the operands are true, then the condition becomes true otherwise false.



-n Checks if the given string operand size is non-zero; if it is nonzero length, then it returns true.






share|improve this answer

















  • 1




    And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
    – l0b0
    Jul 10 at 21:27














up vote
2
down vote













-a is logical AND. If both the operands are true, then the condition becomes true otherwise false.



-n Checks if the given string operand size is non-zero; if it is nonzero length, then it returns true.






share|improve this answer

















  • 1




    And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
    – l0b0
    Jul 10 at 21:27












up vote
2
down vote










up vote
2
down vote









-a is logical AND. If both the operands are true, then the condition becomes true otherwise false.



-n Checks if the given string operand size is non-zero; if it is nonzero length, then it returns true.






share|improve this answer













-a is logical AND. If both the operands are true, then the condition becomes true otherwise false.



-n Checks if the given string operand size is non-zero; if it is nonzero length, then it returns true.







share|improve this answer













share|improve this answer



share|improve this answer











answered Jul 10 at 20:34









SivaPrasath

3,68311636




3,68311636







  • 1




    And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
    – l0b0
    Jul 10 at 21:27












  • 1




    And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
    – l0b0
    Jul 10 at 21:27







1




1




And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
– l0b0
Jul 10 at 21:27




And -f checks if the following word is a regular file. Also, you can use -s to check if a file is not empty.
– l0b0
Jul 10 at 21:27












 

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