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eval.1p (3383B)

    

  1. '\" et
  2. .TH EVAL "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
  3. .\"
  4. .SH PROLOG
  5. This manual page is part of the POSIX Programmer's Manual.
  6. The Linux implementation of this interface may differ (consult
  7. the corresponding Linux manual page for details of Linux behavior),
  8. or the interface may not be implemented on Linux.
  9. .\"
  10. .SH NAME
  11. eval
  12. \(em construct command by concatenating arguments
  13. .SH SYNOPSIS
  14. .LP
  15. .nf
  16. eval \fB[\fIargument\fR...\fB]\fR
  17. .fi
  18. .SH DESCRIPTION
  19. The
  20. .IR eval
  21. utility shall construct a command by concatenating
  22. .IR argument s
  23. together, separating each with a
  24. <space>
  25. character.
  26. The constructed command shall be read and executed by the shell.
  27. .SH OPTIONS
  28. None.
  29. .SH OPERANDS
  30. See the DESCRIPTION.
  31. .SH STDIN
  32. Not used.
  33. .SH "INPUT FILES"
  34. None.
  35. .SH "ENVIRONMENT VARIABLES"
  36. None.
  37. .SH "ASYNCHRONOUS EVENTS"
  38. Default.
  39. .SH STDOUT
  40. Not used.
  41. .SH STDERR
  42. The standard error shall be used only for diagnostic messages.
  43. .SH "OUTPUT FILES"
  44. None.
  45. .SH "EXTENDED DESCRIPTION"
  46. None.
  47. .SH "EXIT STATUS"
  48. If there are no
  49. .IR argument s,
  50. or only null
  51. .IR argument s,
  52. .IR eval
  53. shall return a zero exit status; otherwise, it shall return the exit
  54. status of the command defined by the string of concatenated
  55. .IR argument s
  56. separated by
  57. <space>
  58. characters, or a non-zero exit status if the concatenation could not
  59. be parsed as a command and the shell is interactive (and therefore did
  60. not abort).
  61. .SH "CONSEQUENCES OF ERRORS"
  62. Default.
  63. .LP
  64. .IR "The following sections are informative."
  65. .SH "APPLICATION USAGE"
  66. Since
  67. .IR eval
  68. is not required to recognize the
  69. .BR \(dq--\(dq 
  70. end of options delimiter, in cases where the argument(s) to
  71. .IR eval
  72. might begin with
  73. .BR '-' 
  74. it is recommended that the first argument is prefixed by a string that
  75. will not alter the commands to be executed, such as a
  76. <space>
  77. character:
  78. .sp
  79. .RS 4
  80. .nf
  82. eval " $commands"
  83. .fi
  84. .P
  85. .RE
  86. .P
  87. or:
  88. .sp
  89. .RS 4
  90. .nf
  92. eval " $(some_command)"
  93. .fi
  94. .P
  95. .RE
  96. .SH EXAMPLES
  97. .LP
  98. .nf
  99. foo=10 x=foo
  100. y=\(aq$\(aq$x
  101. echo $y
  102. \fB$foo\fR
  103. eval y=\(aq$\(aq$x
  104. echo $y
  105. \fB10\fR
  106. .fi
  107. .SH "RATIONALE"
  108. This standard allows, but does not require,
  109. .IR eval
  110. to recognize
  111. .BR \(dq--\(dq .
  112. Although this means applications cannot use
  113. .BR \(dq--\(dq 
  114. to protect against options supported as an extension (or errors reported
  115. for unsupported options), the nature of the
  116. .IR eval
  117. utility is such that other means can be used to provide this protection
  118. (see APPLICATION USAGE above).
  119. .SH "FUTURE DIRECTIONS"
  120. None.
  121. .SH "SEE ALSO"
  122. .IR "Section 2.14" ", " "Special Built-In Utilities"
  123. .\"
  124. .SH COPYRIGHT
  125. Portions of this text are reprinted and reproduced in electronic form
  126. from IEEE Std 1003.1-2017, Standard for Information Technology
  127. -- Portable Operating System Interface (POSIX), The Open Group Base
  128. Specifications Issue 7, 2018 Edition,
  129. Copyright (C) 2018 by the Institute of
  130. Electrical and Electronics Engineers, Inc and The Open Group.
  131. In the event of any discrepancy between this version and the original IEEE and
  132. The Open Group Standard, the original IEEE and The Open Group Standard
  133. is the referee document. The original Standard can be obtained online at
  134. http://www.opengroup.org/unix/online.html .
  135. .PP
  136. Any typographical or formatting errors that appear
  137. in this page are most likely
  138. to have been introduced during the conversion of the source files to
  139. man page format. To report such errors, see
  140. https://www.kernel.org/doc/man-pages/reporting_bugs.html .